diff --git a/sbp.cabal b/sbp.cabal
--- a/sbp.cabal
+++ b/sbp.cabal
@@ -1,5 +1,5 @@
 name:                  sbp
-version:               4.13.0
+version:               4.14.0
 synopsis:              SwiftNav's SBP Library
 homepage:              https://github.com/swift-nav/libsbp
 license:               MIT
diff --git a/src/SwiftNav/SBP/Imu.hs b/src/SwiftNav/SBP/Imu.hs
--- a/src/SwiftNav/SBP/Imu.hs
+++ b/src/SwiftNav/SBP/Imu.hs
@@ -44,11 +44,13 @@
 -- gyroscope readings. The sense of the measurements are to be aligned with
 -- the indications on the device itself. Measurement units, which are specific
 -- to the device hardware and settings, are communicated via the MSG_IMU_AUX
--- message. If using "time since startup" time tags, the receiving end will
--- expect a `MSG_GNSS_TIME_OFFSET` when a PVT fix becomes available to
--- synchronise IMU measurements with GNSS. The timestamp must wrap around to
--- zero when reaching one week (604800 seconds).
---
+-- message. If using "time since startup" local time tags, the receiving end
+-- will expect a `MSG_PPS_TIME` regardless of GNSS fix state. This also
+-- requires that the MSG_PPS_TIME message be sent prior to any IMU RAW
+-- messages that are based on the current (as measured at the PPS edge) local
+-- time timestamps. The local time (as defined in the MSG_PPS_TIME message)
+-- must wrap around to zero when reaching the extent of the u64 "Local time in
+-- microseconds" parameter.
 -- The time-tagging mode should not change throughout a run.
 data MsgImuRaw = MsgImuRaw
   { _msgImuRaw_tow :: !Word32