Most of them don’t. Only two have them as a forced complication, one (Sapienza) of which is 15 minutes (which you really don’t need), the other is Sniper Assassin Miami, which I regret I wish I made it optional or longer. (My thinking was if I put a timer in then that would rule out people running across the map to kill someone the old fashioned ways, cos they wouldn’t have enough time if they went to all the targets in person)
All the rest don’t have them or they’re optional, so think of your first run (failing the optional timer objective), as a practice run to figure out what to do! Then once you know just go back and do it again
The ‘bonus’ missions (Podium Sniper, Rooftop Sniper) are designed to be more difficult, and because I noticed that IO has a thing for featuring contracts which have forced complications, so I figured I should make a couple sniper contracts with some.