Draytek Vigor2500V Manual page 91

Call Schedule
On the Time Setup menu, if you press Inquire Time button, the router's
clock will be set to current time of your PC. The clock will reset if you power
down or reset the router so you may prefer to use an NTP server on the
Internet (a time server) to update the clock automatically. NTP updates only
occur when the router is online to the Internet; they will not trigger calls
themselves.
You can have up to 15 entries of different schedules and you must then apply
the required schedule(s) to the appropriate ISP by entering the schedule
number into the ISP setup:
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