If you have some spiritual goal with this meditation then you have to do it daily till you achieve that or feel you need to move onto other meditations. People should have a meditation program everyday (including the final Rtr) where there is certain things you do then alternate it or move to other meditations or add and remove things as needed for progress.
If a person doesn't do a meditation daily (or meditate at all every day)unless it was a working for a specific number of days then both the meditation and the person doing it slowly begins to lose power till you are back at square one (that saying lol probably came from the planitary squares or some working like that Origionally and yeah it is easy to mess up on them)