Sending msgs to Set of whatsapp numbers at specified time.

hi.. I have requirement to send message to set of watsapp users by specified time and date.

My requirement templet look as follows

Subject	any subject
time	assume meeting start time
date	meeting date
venue	meeting venue
matter	any message

i have a requiremet for attach file aslo.

and i need to send the above details at specified time and date(automating the send message).

please tell me the ideas to solve the above requirement. i am new to asp.net and this my first project. please guys guide me to solve this. thank you in advance..