Depends if you're making an analogue clock or a digital one.
If you look inside a cheap mechanical timeswitch [1], you'll find a synchronous motor the size of a sugar cube, turning 50 or 60 times a second, then half a dozen plastic gears reducing the rotation to 1 turn per day. AC wall clocks follow the same principle, but with a slightly different gear ratio.
This means you don't need a printed circuit board, or any integrated circuits, or anything like that. Such efficiency is how you make a profit, if you're selling timers on Aliexpress for $3.50.
If you're making a digital timeswitch, a quartz crystal might be cheaper, or might not - it depends on the insulation/isolation you think your product requires.
If you look inside a cheap mechanical timeswitch [1], you'll find a synchronous motor the size of a sugar cube, turning 50 or 60 times a second, then half a dozen plastic gears reducing the rotation to 1 turn per day. AC wall clocks follow the same principle, but with a slightly different gear ratio.
This means you don't need a printed circuit board, or any integrated circuits, or anything like that. Such efficiency is how you make a profit, if you're selling timers on Aliexpress for $3.50.
If you're making a digital timeswitch, a quartz crystal might be cheaper, or might not - it depends on the insulation/isolation you think your product requires.
[1] http://swarfer.co.za/rc/03-timer.php