Taking tribulus before bedtime isn't a good idea, as it can be stimulating. The only way to know if your testosterone is indeed low is to get it tested regularly over a month, so you know you're not testing at an unusually low moment. Most men, for example, have the highest levels early in the morning, so if that was the only time you tested it would seem high. Doctors usually only test once, which doesn't tell you much, since the levels change over time.