there is certainly a range of time to be ready to take them.off I have cooked 12 racks at once and have had as much as a 30 min difference between the rib on the top rack vs ribs on the bottom rack. i have had ribs finis in 3.5 hrs and other times take 5 hours.
there are many variables to nail down get specific times. the biggest thing IMHO is maintaining an even temp throughout the cook. i have learned to go with the flow(so to speak). I don't fight my smoker to get a specific temp. i may try and get to 225 but if it's running smooth at 240. i just go with 240 and know that meat will cook faster, the hot spots will be dryer.
keeping a steady temp is the best step forward.
second is no peeking. keep that heat in.I see you have a
wsm in your profile. maybe you can reach out to guys that use that smoker for specific tips. fire control and smoke control
i will just sum up how i do it. after many trail runs and reviewing the messages on here there are a dozen ways to get good ribs. anything home made will be good. this is just what works for me on my smoker.
i rub the ribs with olive oil. just a little like 1 tsp per side.
put the rub on and then let sit for 45min to 1 hour while i get the smoker going.
get even temps and setup smoke for 3 hrs worth.
toss in smoker no peeking for at least 2 hours.
check to see if they need some mopping. poke with toothpick(between ribs) see where they are.
every 30mins-1 hr more depending on temps. mop/check if necessary to put sauce on .
i use olive oil as base.i find that the ribs stay very moist when i'm not foiling so i can go a few hours without mopping. some days(at lower temps) I didn't even mop. use sparingly but cover completely. too much oil has thrown off the taste of the rub in past runs.
many way to go with prep and mopping/spritzing) etc. master the smoker. control your heat and amount of smoke and the rest is just paying attention and relaxing.