We re based in Hong Kong. When we schedule a time for our email to go out it gives the date then hours and states CST. Which we assumed was Central Standard Time. However the emails are actually sent out using exactly the same hours but Hong Kong time (GMT +8 hours). For example we program the email to go out 8.10am CST (according to what it says on your website) and the email will be sent out 8.10am Hong Kong time (GMT +8). This must be confusing for overseas users, although we just ignore the CST now. Thought this may be useful for you.
Thank you for reaching out to the Community! I can understand how confusing this change in timezone can be. As you mentioned, when the email is received the time itself is correct. This display change in timezone when scheduling is caused due to the abbreviation of the time zone. Both Google and Constant Contact abbreviates GMT time zones to CST.