Interval based program


Hi Guys,
I am newbie to Ruby P.ming Language. I want to send mail to
the service providers frequently.time will be set by service providers.
We have 100 different service providers, each of them will set their own
time to receive their report email.among the 100 different service
providers 10 or 20 service providers only might get email,that means
they only set their email ids and time lines.others might set their
information later or may not.some service provider those are in the
generating list might get remove from the list.this will be happen from
the front end based on the time lines set by service providers,
we have to send email.

for ex :if one service provider set his time line to receive email at
once in a day, then we have to send email to him once in a day
frequently.he might update that time line meanwhile from the front end
admin while changing his time from front end admin, we have to
update the interval without affecting the original process.

so if anybody have the ideas or if anybody done this kind of task
earlier please give me the ideas.