@ucbalumnus College Placement tries hard not to overload anyone. The kids request 3 letters, but only need 2, sp CP rations them so that the heaviest hit teachers aren’t overwhelmed. That said, if you teach STEM, and particularly Juniors, you’re going to get a lot. Those teachers who have 30 or more (and, yes, that’s been me plenty of times) have the whole summer.
Personally, I can’t do more than 2 at a single sitting or they’re going to start sounding too similar. So some years, that’s how I start my summer mornings, doing 2 letters a day.