Building on Tom's reply, it seems like you could check to see if all of the files are there.
If they are, then you go about your dts package, and at the end execute a sql task which sets the job start time to it's normal start time using sql proc sp_update_jobschedule.
If they aren't, then use sql proc sp_update_jobschedule to how ever many minutes in the future you want.
If the files aren't there by a certain time, then send email, and then reset the start time of job.
Seems pretty simple and you won't have to learn DMO.
David