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 Shares
As you configure, edit or just browse one of your Data Warehouse shares in Funnel you will likely 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 schedule time in UTC without any timezone information. This means that run times of shares will always be in the same UTC time but local run times might vary depending on local daylight saving variations.
To always run the share the same local time just select a Time zone from the list when editing a share.