In File Transport you can create a WHERE criteria to limit the files being processed.
This criteria is converted into CAML and is evaluated at the server. It is therefore the most effective way to specify a criteria, if you can live with the CAML limitations :-)
(on the other hand you can use the File Selection criteria which is by far more advanced but will download all item metadata and evaluate the filter locally)
In the below example I use a parameter to calculate the DateTime 24 hours ago from now and just reference it in the WHERE criteria