currency is not a thing of "28 days i am current, 29 I am not" it it a thing that "leaks" away, If you have not flown (or flown a particular type/procedure) for a couple of days then you may not need much extra brain power, if the lay off is a couple of weeks then you will probably need to think a little more, a couple of months will need a definite application of the grey matter - more than this really needs study and maybe a bit of proper practice depending on what you are trying to do. Whatever you are up to, you need to think how long ago you practised it last and how much you might have lost in that period.
