In the Origins Update Bulletin for the 17th of July, 601.5 was removed and essentially replaced by 601.2e, so the legality of casting a spell, including timing issues, is now part of the casting process instead of being a prerequisite of starting to cast a spell.

However, the rules of suspend did not change ("If you could begin to cast this card by putting it onto the stack from your hand, you may pay and exile it with N time counters on it. This action doesn't use the stack.")

In a vacuum, I would say that it means that it is now possible to suspend any spell at any time a player has priority, but this would be a big change, and nobody talked about it. So, I'd like some confirmation about the situation here.

Asked Rules Manager Matt Tabak: “Nothing has changed about how Suspend works.”