Q. Can I give money to a family that needs it before Purim, and it should be counted as Matanot Laevyonim since they need it for Purim expenses, usually bought before Purim?
A. Shulchan Aruch (O.H. 695: 4) mentions Matonos Laevyonim as a mitzva that pertains to Purim and should be complied with on that day. Therefore Horav Shlomo Miller’s Shlit’a opinion is that for the money to be included in this particular mitzva it should be given on Purim itself. If given before, it should be with the condition that it be held as a pikadon or deposit in trust by the receiver, to be obtained (koine) and used on Purim itself. If it is a post-dated cheque, it should be given also on the same terms, as the post-dated cheque could be exchanged now.
Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit"a