"Realism" is that when your life is on the line, you do what you have to in order to stay alive.
Mountain climbers routinely practice a degree of methodical caution which IMO is way more inconvenient than chanting for six seconds every minute. Some of it's vocal: on belay, belay on, climbing, climb on, then ongoing requests for more or less slack. If that would drive you insane, then I strongly recommend you avoid technical climbing.
I've heard military patrolling or escorting a convoy described as boredom combined with terror, for hours on end, because any one of those humdrum moments could be the moment before a mine or an ambush, and maybe, just maybe, keeping your eyes moving might keep you (and your comrades) alive. Yes, by civilian standards, that's hard on sanity. There's a reason some veterans have a difficult transition back to civilian life and NOT scanning every rooftop for snipers.
I've done some rock climbing. I would chant, six seconds every minute, if I were at risk of a fatal fall and chanting could reduce that risk. From what I've heard of military situations, chanting for 6 every 60, to have a better chance on init when an ambush starts, would be a drop in the bucket, as an addition to the level of mental fatigue that's inherent to hostile-territory patrol or convoy missions.
Is dungeoneering less tense? Varies. He-Man sneaking into Skeletor's lair, not so tense. Gandalf and Aragorn in the Mines of Moria, yes, that tense. (Pippin, meanwhile, was in the bored-civilian frame of mind, even after the Watcher in the Water's tentacle attack. "Fool of a Took!")
Strain on voice? Hah. Anyone who works in a call center is using their voice much more than 10% of the time, all day long except for a Short Rest at lunch hour.
None of that means you have to allow a cleric to maintain Guidance. You want a cool-down? Sure, just as there is for Augury and so forth. For gameplay reasons, or for how-divine-magic-works reasons. For realism? No way.