diff --git a/bin/reth-bench/README.md b/bin/reth-bench/README.md
index e63f73875d..601b52f28e 100644
--- a/bin/reth-bench/README.md
+++ b/bin/reth-bench/README.md
@@ -32,7 +32,7 @@ Otherwise, running `make maxperf` at the root of the repo should be sufficient f
 The `reth-bench new-payload-fcu` command is the most representative of ethereum mainnet live sync, alternating between sending `engine_newPayload` calls and `engine_forkchoiceUpdated` calls.
 
 The `new-payload-fcu` command supports two optional waiting modes that can be used together or independently:
-- `--wait-time <duration>`: Fixed sleep interval between blocks (e.g., `--wait-time 100ms`)
+- `--wait-time <duration>`: Fixed sleep interval between blocks (e.g., `--wait-time 100ms` or `--wait-time 400` for 400ms)
 - `--wait-for-persistence`: Waits for blocks to be persisted using the `reth_subscribePersistedBlock` subscription
 
 When using `--wait-for-persistence`, the benchmark waits after every `(threshold + 1)` blocks, where the threshold defaults to the engine's persistence threshold (2). This can be customized with `--persistence-threshold <N>`.
diff --git a/bin/reth-bench/src/bench/helpers.rs b/bin/reth-bench/src/bench/helpers.rs
index 8813082156..b9ae67d910 100644
--- a/bin/reth-bench/src/bench/helpers.rs
+++ b/bin/reth-bench/src/bench/helpers.rs
@@ -2,7 +2,10 @@
 
 use crate::valid_payload::call_forkchoice_updated;
 use eyre::Result;
-use std::io::{BufReader, Read};
+use std::{
+    io::{BufReader, Read},
+    time::Duration,
+};
 
 /// Read input from either a file path or stdin.
 pub(crate) fn read_input(path: Option<&str>) -> Result<String> {
@@ -51,6 +54,22 @@ pub(crate) fn parse_gas_limit(s: &str) -> eyre::Result<u64> {
     let base: u64 = num_str.trim().parse()?;
     base.checked_mul(multiplier).ok_or_else(|| eyre::eyre!("value overflow"))
 }
+
+/// Parses a duration string, treating bare integers as milliseconds.
+///
+/// Accepts either a `humantime` duration string (e.g. `"100ms"`, `"2s"`) or a plain
+/// integer which is interpreted as milliseconds (e.g. `"400"` → 400ms).
+pub(crate) fn parse_duration(s: &str) -> eyre::Result<Duration> {
+    match humantime::parse_duration(s) {
+        Ok(d) => Ok(d),
+        Err(_) => {
+            let millis: u64 =
+                s.trim().parse().map_err(|_| eyre::eyre!("invalid duration: {s:?}"))?;
+            Ok(Duration::from_millis(millis))
+        }
+    }
+}
+
 use alloy_consensus::Header;
 use alloy_eips::eip4844::kzg_to_versioned_hash;
 use alloy_primitives::{Address, B256};
@@ -270,4 +289,24 @@ mod tests {
         assert!(parse_gas_limit("G").is_err());
         assert!(parse_gas_limit("-1G").is_err());
     }
+
+    #[test]
+    fn test_parse_duration_with_unit() {
+        assert_eq!(parse_duration("100ms").unwrap(), Duration::from_millis(100));
+        assert_eq!(parse_duration("2s").unwrap(), Duration::from_secs(2));
+        assert_eq!(parse_duration("1m").unwrap(), Duration::from_secs(60));
+    }
+
+    #[test]
+    fn test_parse_duration_bare_millis() {
+        assert_eq!(parse_duration("400").unwrap(), Duration::from_millis(400));
+        assert_eq!(parse_duration("0").unwrap(), Duration::from_millis(0));
+        assert_eq!(parse_duration("1000").unwrap(), Duration::from_millis(1000));
+    }
+
+    #[test]
+    fn test_parse_duration_errors() {
+        assert!(parse_duration("abc").is_err());
+        assert!(parse_duration("").is_err());
+    }
 }
diff --git a/bin/reth-bench/src/bench/new_payload_fcu.rs b/bin/reth-bench/src/bench/new_payload_fcu.rs
index 086e997158..36a4f51dbc 100644
--- a/bin/reth-bench/src/bench/new_payload_fcu.rs
+++ b/bin/reth-bench/src/bench/new_payload_fcu.rs
@@ -12,6 +12,7 @@
 use crate::{
     bench::{
         context::BenchContext,
+        helpers::parse_duration,
         output::{
             write_benchmark_results, CombinedResult, NewPayloadResult, TotalGasOutput, TotalGasRow,
         },
@@ -25,7 +26,6 @@ use alloy_provider::Provider;
 use alloy_rpc_types_engine::ForkchoiceState;
 use clap::Parser;
 use eyre::{Context, OptionExt};
-use humantime::parse_duration;
 use reth_cli_runner::CliContext;
 use reth_engine_primitives::config::DEFAULT_PERSISTENCE_THRESHOLD;
 use reth_node_core::args::BenchmarkArgs;
@@ -40,6 +40,9 @@ pub struct Command {
     rpc_url: String,
 
     /// How long to wait after a forkchoice update before sending the next payload.
+    ///
+    /// Accepts a duration string (e.g. `100ms`, `2s`) or a bare integer treated as
+    /// milliseconds (e.g. `400`).
     #[arg(long, value_name = "WAIT_TIME", value_parser = parse_duration, verbatim_doc_comment)]
     wait_time: Option<Duration>,
 
diff --git a/bin/reth-bench/src/bench/replay_payloads.rs b/bin/reth-bench/src/bench/replay_payloads.rs
index 171615deec..0ee04a56d0 100644
--- a/bin/reth-bench/src/bench/replay_payloads.rs
+++ b/bin/reth-bench/src/bench/replay_payloads.rs
@@ -14,6 +14,7 @@
 use crate::{
     authenticated_transport::AuthenticatedTransportConnect,
     bench::{
+        helpers::parse_duration,
         output::{
             write_benchmark_results, CombinedResult, GasRampPayloadFile, NewPayloadResult,
             TotalGasOutput, TotalGasRow,
@@ -30,7 +31,6 @@ use alloy_rpc_client::ClientBuilder;
 use alloy_rpc_types_engine::{ExecutionPayloadEnvelopeV4, ForkchoiceState, JwtSecret};
 use clap::Parser;
 use eyre::Context;
-use humantime::parse_duration;
 use reth_cli_runner::CliContext;
 use reth_engine_primitives::config::DEFAULT_PERSISTENCE_THRESHOLD;
 use reth_node_api::EngineApiMessageVersion;
@@ -78,6 +78,9 @@ pub struct Command {
     output: Option<PathBuf>,
 
     /// How long to wait after a forkchoice update before sending the next payload.
+    ///
+    /// Accepts a duration string (e.g. `100ms`, `2s`) or a bare integer treated as
+    /// milliseconds (e.g. `400`).
     #[arg(long, value_name = "WAIT_TIME", value_parser = parse_duration, verbatim_doc_comment)]
     wait_time: Option<Duration>,