Depending on the psecies, or cultivar, there can be two to three weeks between those that are early (Little Princess, Katsura, Orange Dream among others) and those that leaf out late (in my garden, Osakazuki, Sango Kaku, Acer monspessulanum, etc).
Here are some flowers showing on 'Phoenix', that is just going out of dormancy whereas 'Orange Dream' has been in full leaves for over two weeks :
And here's one that I've never seen in garden centres or even at plant fairs, it was labelled "Acer sinensis", but it is not a registered name and "Acer sinense" has leaves that look different. And since the plant fair wasn't open to the public yet, I suppose that the owner was looking around and chatting with colleagues, like me : our club displays about 20-25 bonsai there each year.
Anyway, on this one, the flowers are very visible, much more than on most species I know :
