In Raidou's canon, it is "detrimental" to stay too long in a timeline that isn't his, but meeting himself specifically doesn't seem to be much of an issue. The worst that happened was that his counterpart thought he was an impostor and had to be talked out of attacking him. And then he was sent on a fetch quest.

...Raidou's canon also features Japan launching a satellite into space (in 1931), which results in Neil Armstrong being condemned to wander eternally outside of space and time as a lost soul. (The satellite ends up being blown up by Raidou's mentor and one of his demons after they're launched into space in a homemade rocket to take it down. Again, in 1931. The first DSRK game is really, really weird sometimes.)