You don't have to since sockets are carried over when evolving (I'm pretty sure someone confirmed it here) but keep in mind he'll gain an extra socket when he's evolved. There's always the possibility that you'll gain a socket you'll want to keep but are unable to since you already have 3 sockets.
Hm, yeah, that'd be annoying. In that case I might socket QCK iva this time and evolve INT iva asap and get him next time
getting 5/5/5 and then having to get a million Ivas next time for the last 5 sounds like a nightmare