Can anyone help me with the following query.

I need to write a piece of code that will allow me to carry out the
following function or is there something already out there?

I want to e-mail a defined group of contacts a simple message: "It's time to
Upload your scanner now please.", and need it to be recurring at 15-minutes
past the hour between 06:00 and 20:00 hours.

I am sure that it must be achievable because the IMP.Task form that already
exists, but that only allows for a recurrence to be set on a daily basis and
I can't work out how to change the frequency.

Please help!