It depends. Sometimes RENFE uploads it
early, sometimes it makes it very late. Anyway, in early June it should be posted but, of course, they can upload it earlier. Another point to consider is that sometimes they upload a partial schedule (i.e.: including just some of the trains available) and later they upload the schedule of the missing trains. That's why it's a good idea to check the current schedule so you can get an idea of how many trains you should find once the summer one is published (and you can get an idea too of the departure times because they'll be almost the same -if not the same- with the summer schedule).
In other words, you have two main options:
- Check daily the web of RENFE till you find the schedule published and the booking time opened so you can book your tickets as soon as the bookings are opened. Personally, I wouldn't bother to check more than 60 days in advance.
- Wait till early June where it's almost sure the new schedule will be already published (only if RENFE is really late the schedule may be published later, i.e. around June 10th, but it might happen) and the bookings opened. The downside is that if RENFE uploads early the schedule this year some of the discounted fares might be sold out by early June.