Blue Tits Proximity ?

A long apparently unused nest box quite high up on a tree a few yards from my back door, has this year for the first time been utilised by Bluetits. First noticed a couple of weeks ago, have seen 2 taking turns in there. They've been pretty busy but my concern is that as it is so close to my main entrance, whether our comings and goings might frighten them off. One of them was very very circumspect about going in this morning after I'd been in the garden. I could potentially utilise another door, though that'd be pretty inconvenient. I suppose my question is, how comfortable are they generally with people around from time to time. I'd hate to think that they might abandon eggs, or chicks because of our activities...any advice welcome. !