Epic hero tokens – where do you spend yours?

[Dudeious.Maximus]

Saving Epic Hero tokens – which Summons can they be used for?

Looked around but couldn’t find anything concrete so sorry if this is obvious but should I use my epic hero tokens right when I get them or is it possible to use them on some events? I saved them for Atlantis but they can’t be used there. I just started playing during the Santa event but I didn’t know what was going back then and I def don’t remember how the summon worked.