I think that is right in general but I keep seeing exceptions, e.g. today at the 9:10 Tamworth race I placed a fill / kill offset bet 10 secs before the off and it was taken just before the in-play suspension with the offset being placed in-play.
26/01/2024 09:09:51: [G_Auto 1] : £ x.xx Lay bet placed on 6. Superbon at 8.2. Entirely unmatched when it initially reached the market. Ref: 336061526039 ( Fill or kill bet with 120 seconds delay. Offsetting by 5 ticks with greening. )
26/01/2024 09:11:10: Guardian has detected that the market is suspended
26/01/2024 09:11:11: Guardian has detected that the market is in-play
26/01/2024 09:11:11: Guardian has detected that the market is now unsuspended
26/01/2024 09:11:11: [G_Auto 1] : £ x.xx of unmatched bet (Ref:336061526039) was filled before remainder was killed.
26/01/2024 09:11:13: [G_Auto 1] : £ x.xx Back bet placed on 6. Superbon at 9.2. Entirely unmatched when it initially reached the market. Ref: 336061630921
Strangely the log shows the initial bet being taken after after the suspension but it looked to me (visually) that it was taken before & if it wasn't it should have been cancelled by the in-play suspension...
Either way something strange happens just before the off and it happens quite often.