Blue Tit update

It's been about a week and a half now and the pair of Blue Tits in my back garden are becoming increasingly confident about being in their new home.
Previously they have only spent a fleeting moment inside after a lot of hesitation about going in.
I haven't seen any nesting material being taken inside but today one of the birds spent roughly 10 minutes inside occasionally popping their head out to look around. Maybe there is some construction going on in there and I missed the nest material going in.
There has been some behaviour I have noticed.
For one the Blue Tits have become territorial, particularly against their once friends, the Great Tits.
Also, the male and female Blue Tit don't like being in the box at the same time. If one flies in on the other they shoot straight out.
I'll keep you posted if something a bit more interesting happens....