Sewers - I get sewer gas in the bathroom but only in the evening and nighttime hours?

I get sewer gas in the bathroom but only in the evening and nighttime hours?

Any plumbers out there for a suggestion as to what it is?

MAYBE YOU HAVE A LEAK IN THE PIPE OR SOMETHING HAS IT PLUGGED. GOOD LUCK WITH THIS.
sounds like you are loosing your trap seal sounds like you are on town sewer if so you should look into a house trap .. it could be in a bathroom you don't use alot try running those fixtures every couple of days to keep all of your traps primed
Report it to health and safety.That is what they are there for.
Well, were do you live, Is it getting cold at night and you use the heat. Its sounds like a possible negative pressure problem created by your heater...if your even using one. Its sounds like that negative pressure is pulling the gas back out of the stink pipe. Kick your heater on or blower and see if that creates the smell.
some of your traps are draining, so get to all your traps and fill them, check all as you fill to see if leaking(use a friend) if not that, check the pipes under your bedrm and mstr bath in the basement,, its possible one froze if you had bad weather and is leaking near and under your bdrm area. ...this is a shot in the dark w/o being there.... hope it gets better for ya