Data collection
When Funnel retrieves data from the sources you have connected, the data is attributed to calendar days. The definition of day for each source will be depending on the originating platform and your settings there.
I.e. if you set up your Facebook Ad Accounts to use Pacific Standard Time (PST) the definition of "January 1 2018" for those sources will be according to the PST time zone. Funnel can not "convert" between time zones.
It's also worth noting for data collection that the previous "day" of data is very rarely complete at the source early in the next day, and in many cases the data will keep changing for up to 30 days.
Data Warehouse Exports
As you configure, edit or just browse one of your Data Warehouse exports in Funnel you will come across the schedule time for it. This time is presented differently depending on where you are in the world. In my case, it will look like this:
By default, Funnel will save the schedule time in the user's time zone.
When exports calculate which date range to export, it will perform this calculation in UTC. For example, if you have scheduled your export to run at 1:00am CEST (which would be 11:00pm UTC) and with the date range of "yesterday", this would export the day before yesterday.