Could I ask why you want to use the conference time as the first entry? Do you often want to search the hash for conferences at an exact time? (The hash won't help you searching conferences in eg. an interval between two given times, which is what you'd more often want.) If not, why don't you just use a single array of hashes, with each entry of the array storing one conference, and the time stored in another field just like how you store the conference name and type and comment.

Update: oh, I see kyle has already suggested this.