For consumer routers, not really; there's no demand as they're low-power draw devices (my 54GC uses 3W@idle). Depending on the device you may be able to configure access for certain times of the day.
If you build a PC-based router, you could use WOL, but power efficiency would be the last reason to go that route.
Not a real hibernation, but plug it into a lamp timer.
How do you configure access for certain times of the days?
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