The videos and simulations I've seen suggest the reentry burn lasts 30 seconds.
This is followed by the final landing burn and it may be preceded by a boostback burn.
I'm interested only in the reentry burn: Is it always 30 s? Is it a timed burn, or is programmed to last until some constraint is met---e.g., when some target velocity or altitude is reached?
Would 45 s be too long for a reentry burn?