If there's no damage, it doesn't take that long. We had a blackout in 2009 in which the national grid of two countries (Itaipu is shared between Brazil and Para

If there's no damage, it doesn't take that long. We had a blackout in 2009 in which the national grid of two countries (Itaipu is shared between Brazil and Paraguay) went down; I'm looking at the official report right now, and it took less than half a day to restore nearly all of the system for this country. Of course, if there's damage beyond the redundancies, it can take much longer; see for instance the recent blackout in the Amapá state, in which two transformers at a key substation were damaged by fire (and the third was under maintenance).