What I ended up doing was creating a rule for every 1/2 hour, and including the sessions that covered that 1/2 hour time, including the longer ones.
ex:
3:00 - 4:00 "AAA Long 1 hour session"
3:00 - 3:30 "BBB 1/2 hour session"
3:00 - 3:30 "CCC 1/2 hour session"
3:30 - 4:00 "DDD 1/2 hour session"
3:30 - 4:00 "EEE 1/2 hour session"
Then I'd have these rules:
Check_300pm - includes AAA,BBB,CCC, min 1 max 1
Check_330pm - Includes AAA,DDD,EEE min 1 max 1
------------------------------
Gene Kaufman
Associate Web Services Manager
Phoenix Contact USA, Inc.
------------------------------