Alright, so on the issue of scheduling, here's what I suggest:
March 20: 16:00-19:00 CET (Delian works, so start an hour later)
March 27: 14:00-18:00 CET (Delian doesn't work, CEST starts, move it forward one hour for Dane)
April 03: 14:00-18:00 (same as above)
April 10: 16:00-18:00 (Start late due to Delian working)
April 17: 14:00-18:00 (no change needed)
April 24: 16-18:00 (Start late due to Delian working)
May 01: 14:00-18:00 (no change needed)
This is assuming that when he says 7-16:00, he means he'll be available at 16.
On a related note, I'll need a sub March 27.