Nesting box

I bought my husband a nesting box with camera for his birthday 2 years ago. Only this year have we had any activity apart from spiders! In an effort to attract birds, hubby turned the box 45 degrees and drilled a hole lower down in the box, with a view to covering the one further up later. However, a pair of great tits have now begun using the box and are using the uppermost hole to enter/exit. I presume it would cause them to abandon the nest if we did anything now. Will this be a problem? They have only started building the nest today.