Indeed speed and how many people go down a path area ll you can control

Say you have a route where there are 2 randomisers you need to hit with 2 paths each - each person going down that route has a 25% chance of getting it 'correct'

Next lets say you have a route that has a rotating arrow, first points to a short path and then a long path. You need to ensure a slower speed squad passes the point 1st - so planning your units order and their speed can be trial and error to a degree

Good news is no time limit on main mission maps, only bad news is you'll likely want to putting lots of time and energy into event maps which have limited time and give limited time content rewards - and some events can be stamina hogs

Not repeating the above, all i am adding is do not worry about it too much, yea the flower gem reward is nice, but move on to higher maps, untill the maps are too hard and then go back for them.
On the event/time limited maps you might struggle to get them three stared, but most of the time this forum has some one who can help you with optimum starting position, and no event so far requires you to three star them for event rewards, they used to but changed it some time ago.
And making sure, you know you can move the groups stating position so they can start from different Tents?