Every date is actually storing time as well and is stamped as UTC 0:00, and then adjusted for time zone. So let's say you set the date April 6th, 2017. That gets logged as April 6th, 2017 0:00:00 EST (UTC +8) into the Clarizen UI. In the database this is stored as April 6th, 2017 8:00:00 UTC. Then when an end user views this date, it gets adjusted for their time zone on their computer. If they are set to UTC +8, then it comes back as April 6th 2017 0:00:00. If the time zone is off either in system settings or the end user's computer, it can offset the dates by one day--so this is something to watch out for.
As for your specific scenario, your working hours might be factoring in. If working hours begin at 8:00:00, then UTC +8 would set this to 16:00:00 UTC. You would then have to convert this number back from UTC to your time zone. Hope this makes sense, I know it can get pretty complicated.