I'm fairly new to hybridizing also but last year I tried to keep good records. I found that most crosses done in the afternoon don't take for me. Days when the temperature is above 90 and it's very humid, I also have most crosses fail. If it rains and the pollen gets wet you can forget about it too. But other than that it seemed like it was pretty random in terms of days when almost all my crosses took and others when hardly anything did. All I can suggest is keep trying.
