How to set the first day of the week?
Sign in to TickTick on the web.
Click the avatar in the upper-left corner of your TickTick homepage, then click "Settings" from the menu that appears.
From the "Start Week On" drop-down menu, choose Saturday, Sunday, or Monday as the first day of the week in TickTick.
Where is it used?
Due date calendar
Mini calendar (see section 2.7.4 for details)