Assuming you got the film into the can correctly and without exposing it to stray light, the only thing that is as or more important is using the correct chemicals, at the right dilutions and in the right order. (Develop / Stop / Fix / Rinse)
Probably the best investment you can make for film developing is a good thermometer and a good timer.
When developing black and white try to hold your temperatures to ±1º C. of the target temperature. That will give you a 2º swing to work inside of. (Yes, 2º is enough to make a noticeable difference.)
If you look on the datasheets supplied by film manufacturers, their times are often listed in increments of 15 seconds. That means you can assume you have a 15 second window to work inside of when it comes to timing accuracy. (Remember, you have to account for the time it takes to pour the solutions into and out of the canister.)
So... In my estimation, if you can hold your temperatures to ±1º and keep your times accurate to less than 15 seconds, you should be fine.
Yes, time and temperature are important but, if you work efficiently in an organized manner and use quality tools you should have no problem keeping your process inside spec.