In 5ed it's stated they take the season to produce and can be repeated later with the same lab text. But they surely aren’t spells (your lab total isn't halved for the ritual being invented in a season, the ritual isn’t designed to reach a total), and they don't need to be cast.
This is the most recent (and fairly complete) discussion I can find in the forums:
All in all, I'd say they are their own thing? Neither spells, neither rituals, neither enchantments. I don’t recall if we have a previous discussion in this saga about Mercurian Magic being applied or not.
A redcap's longevity ritual is designed by someone with a lab total of at least 50 (giving them a +5 bonus since they don’t have the gift). Not making any point, just listing facts that might help us thinking. Maybe it was also discussed before in the saga, I think there was a player who wanted a LR before (but I might be misremembering).
It's late, I'll sleep and take a look tomorrow.