I also seem to have a built in clock for 30 mins 1 hour and two hours at work. Doesn't ever seem to work when I'm not at work or f**king tho, which is a shame.
As for tips I have a galaxy gear you can set up to show the screen when you sort of jiggle it (supposed to be when you snap your wrist but it'd be like a strobe light disco with hand jobs.) . Black strap on a black head board, guys rarely notice it and I can usually get a foot or hand, sometimes my head to wack the screen on if I feel a booking is dragging on. I guess if you have a smart watch it may have a similar feature? I've been known on longer bookings to keep the screen of a spare mobile phone just under the bed with the screen kept on screen saver clock so I can see the clock, just lean over when changing positions or stretching.