When using the Membership Pro -> Subscriptions Management menu type:
When entering a new subscription there are three date fields near the bottom -- Created Date, Subscription Start Date and Subscription End Date. If they are left blank then the resulting date/time values are correct. When I enter dates for these, and save, then the date/time values are out by 8 hours.
For example [Created Date] "2019-02-04" becomes "2019-02-03 16:00:00". 8 hours are subtracted from the date/time.
The Joomla time zone is set to Vancouver (which is UTC - 8). The server was set to UTC but changing it to America/Vancouver (in php.ini) made no difference.
I've attached a couple of screen shots. I'm using Joomla 3.9.2 and Membership Pro 2.16.1