Told in chat that the following obvious and basic use case isn't possible - hoping that there is a solution:

* We're in TimeZoneA and have clients in other time zones

* We hold training sessions with our clients

* When on a phone call we set a time for the training sessions to occur by entering it into a field (as our Zoho is set for TImeZoneA, that meeting time will be stored in TImeZoneA time)

With a blueprint and/or custom function we want:

* an event to be scheduled in our calendar for this meeting (this is no problem)

* an email reminder to our client including the meeting time *in the client's timezone* (supposedly not possible)

Obviously there would need to be a "Time zone" field for the client record but is there no way to make this happen? Are we really supposed to be sending email reminders to our clients who are in TImeZoneC that say "See you for our meeting on X Day at Y time TimeZoneA"?