not much, around 2weeks or so. The bulk is not lost easily as long as you eat relatively properly in your break.
Important tip: if you find yourself in situations where you cant workout for a few weeks it only takes working out once a week but with 90% weight and 6-7 reps with 1-2min intervals (2-3sets) to maintain your max strength levels and since this workout is pretty easy, you can do all muscle groups (you can even use compound exercises like chin-ups, tricept dips, push-ups etc so that the workout takes even less) once and you'll be kept at a stable level for up to 5weeks like this.
I dont think I'll go for a leaning stage this summer, I'm happy with my definition even now and I wanna get even more dense before I attempt to shed all the fat.
My goal is to create such dense muscle ( I dont wanna increase body weight anymore, I'm already big enough for my taste) that even relatively prolonged absence from the gym for whatever reason wont affect my overall fitness level.