You don't have anything to worry about. After spraying, glyphosate needs 6-12 hours of dry weather to dry and be absorbed into the plant. After a couple days, there would be no risk of it splashing off the plants in the rain and onto something you weren't targeting. In addition, if there were any left on the weeds that could move with the rain, the rain would also dilute it, and a heavy rain would wash what was left to the ground. If any active glyphosate were still present, some might splash on non-target plants, but the rain would then wash it off to the ground before it had a chance to soak in.

After a couple days, I would think that either all the glyphosate has been absorbed into the target weeds or would have been degraded through bacteria on the plants themselves or the activity of sunlight, although I don't have any knowledge of how fast this breakdown process works.

I've never seen any migration of the glyphosate when it rains after applying the herbicide, even if the rain happens a short time after spraying. The only problem I've had is ignoring that little cloud on the western horizon that turns into a nice little shower an hour after I spray and I end up with reduced and spotty results.

Thank you so much for the reassuring reply, beeone! I went out to check and so far all my non-targeted plants look healthy and happy.

The USEPA ground water people have found identifiable quantities of glyphosate products far downstream from where they were applied, and several european countries have determined that the manufacturers of these products lied about them going inert, in the formualtions in which they are sold, and so have prohibited sellers of those products form making those claims.
These glyphosate products are not as innocuous as claimed.