It looks like the eggs have hatched after about 16 days of breeding. On May 4th the weight inside the birdhouse started going up. The female will warm the hatchlings and both female and male will feed the young ones from now on. According to Wikipedia the young birds should be ready to leave the nest in about three weeks time (end of May/beginning of June). And it still amazes me how fast all of this is happening :-) .