it seems an unsolvable problem either way, the meeting is "at 12:00 london"

1. the London person owns it, schedules in local (London) time 12:00

2. the London person owns it, schedules mental math explicit Alberta time 05:00

3. the Alberta person owns it, schedules in local (Alberta) mental math time 05:00

4. the Alberta person owns it, schedules in explicit London time 12:00

You cannot get all of these working by software only no matter what you do, because there "mental math" time cannot take into account the implicit expectations, 1 and 4 will be correct as stated (the meeting is at 12 London time) but 2 and 3 what do you do? How would you differentiate between "mental math what I thought Alberta time was" vs "I really meant it at this Alberta time"