From my understanding, it differes greatly between species of otters. Sea otters are able to hold their breath for 4-5 minutes, and can reach a maximum depth of roughly 300 feet, with the deepest dive ever recorded being 318 feet. However, the average dive is under a minute long and the average depth is roughly 60 feet, which would imply that depths greater than 60ish feet would be somewhat uncomfortable or impractical for otters to undertake regularly and only really happen when necessary.
River otters, on the other hand, cannot go nearly as deep or for nearly as long, bottoming out at around a maximum depth of 60 feet per dive. However, they can swim at speeds of up to 7 mph, whereas sea otters usually don't go too much faster than 5-6. River otters can also swim for a quarter of a mile underwater before needing to come up for air, and can hold their breath for around 4 minutes comfortably, with the maximum recorded time sitting at roughly 8 minutes before needing to come up for air.
Looking back, that was a bit more information than you initially asked for, but extra information on otters never hurt anybody!