It took the Great Tit female about a week to build her nest.
And tonight for the first night, she is sleeping in it. Which makes me believe that there is an egg too!
This is based on observations of past years. Great Tit females I have observed in the past started sleeping in the completed nest, only after they had started laying eggs.
As, however, this birdy seems to be going about things slightly differently she might be also ignoring what I just assume is a constant in the Great Tit world.
I will change the camera view tonight and hopefully we will find out soon.
At any rate assuming she did lay an egg we can also just count the days (1 egg/day at most)...and perhaps that will also help.