So not sure if this is relevant to your issue, but here's what I've found.
Every project has a schedule, and times are based on the computer time zone relative to the project schedule. We have project managers in 6 time zones, so we have 6 project schedules defined, all of which start at 08:00 AM and end at 05:00 PM, with a 1-hour break, and a work day of 8 hours in project preferences. When I create a project, I select the project schedule corresponding to the time zone of the assigned project manager, so that when they enter a 1-day task starting at 08:00 AM, it will start and end on the same day. At project creation, I start the project at 08:00 AM my time relative to the project schedule: I'm in PST, so if the project schedule is EST, I start the project at 05:00 AM. Ditto with tasks that I add to that project - 5 AM start. If I entered an 8:00 AM start on a 1-day task on project with an EST schedule, it would actually start at 11:00 AM and end the next day. ~Jeff