If someone does lets say a love spell on friday for a week, since friday is the day of venus which is ruled by love. If you continually burned the candle the rest of the week would it have any effect if it was burning on saturday which is ruled by saturn and tuesday ruled by mars? You shouldn't do love work on those days, would it still have the venus energy if casted on friday?
When you do a love spell; say on a candle, and you happened to do it on a Friday (day of love/i.e. Venus-love) then yes that energy and magick was placed into the candle, just note that when you use it for love on the next day of course the magick won't be so great/not at all depending on how much you used it.
And if you never used it till the next Friday it would still be the same. Heck as long as the energy is still there, it would be there for your love in a year.