When creating templates using Memo you can set the time of day the message will be sent out. The time zone used for this is the time zone at the guide location and will be set automatically. You can check the time zone for each guide (and manually update it in the rare case of errors) from the Guide Details tab for each guide.
Note that when viewing the timing of scheduled messages, the time displayed will be adjusted according to the time zone of your local device. In most cases this will be the same as your guide time zone but be aware if you are not physically in the same time zone as your guide location then the scheduled time may appear different. But the sending time is always based on the time zone of the guide, which is set according to the location of the home pin as shown on the guide book map.