What do you mean with rain and time? You posted in indoor growing, so I assumed your plants would not get rain. But this is good because the rain should help wash any sulphur off. I would think that your buds would be fine in 3 weeks, especially if they get rained on from time to time. If it doesn't rain, I would definately gently wash the buds at least once. This will knock off a few of the trichomes, but most will be there for your smoking pleasure.