The Rule
Attend To How You Describe Time
It's very easy to get lazy and say "a few minutes" without really conceiving of how much time "a few minutes" can feel like under specific circumstances—and it's also very easy (and a weirdly common 372 trope) to go the other way and describe time very precisely, like "14 seconds later". Very precise times are probably more disruptive to the reading experience because they invite the reader to scrutinize them, but inaccurate ranges will also trip up careful readers. Phrase things in a way that encourage the reader to stage things naturally in his own mind: Use precise times only when the situation demands it (some action or suspense scenes, e.g.).