Donald,

Great comments. Actually in current usage, Becquerel development can be done in about 2 hours using amberlith or rubylith with either a 500watt light or direct sunlight. Since Becquerel plates don't benefit from bromine fuming it is a simpler process, but about 2.5 stops slower. Also, Iodine doesn't have to be heated. The fumes created at room temperature are enough.