If it's an instant HW heater (and, um, *WHY* are you heating HOT WATER?!?!) it should only turn on when hot water is demanded. That's the way it's supposed to work...
Intermatic 1-hour wind-up timer, the same kind you find on the bathroom lights or the spa jets at any apartment or condo. They are rated for 20 Amps resistive load, and they replace a wall switch.
(Also available in 15-minute, 30-Minute, 2 Hour, 6 Hour. For your purposes getting the one with the 'Hold' feature is OK, for when you throw a party and want it to stay on all evening. If it's a public restroom you do NOT want the Hold feature so the lights can't get left on. They come both ways, read the box.)
Wind the knob and flush through some fresh water through the Insta-Hot when you get up, and by the time you get out of the shower and dressed you'll have hot water all ready for tea.
The timers are readily available at any Borg (Home Depot, Lowe's, True Value, Ace, supply house) but you'll have to put it in a metallic junction box under the sink.
Hopefully you already have the needed "Split-wired" receptacle under the sink on the disposal circuit - one side of the duplex receptacle under the sink is on constantly, and the other side is switched for the garbage disposal. If not, get it rigged this way along with an outlet on the dishwasher circuit - and then you'll always have two "extra" coffee-urn or warming tray circuits with outlets the next time you throw a big party.
(Just don't try running the dishwasher or disposal till after the party, or unplug those coffeepots for a few minutes.)
Get two "cord grip" clamps and a 6' 12-gauge grounded extension cord. You cut the cord in the middle, put the ends through the cord grip into the box and cinch them down. Black wires go to "Line" and "Load" of the timer, white wires get spliced with a yellow wire nut. The Green wires get T-spliced (strip one wire longer than the other) with a bare barrel crimp "ground splice" and the 1" longer end of one ground lead goes into a crimp spade lug. The spade lug is bonded to the metallic box with a 10-32 ground screw.
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