Re-entry visa is the document allows you to cross the border when you are entering the Republic of Ireland. It is in a form of a label on a full page on your passport.
Since it is the document for crossing the border when entering, you don't need a re-entry visa if you don't need to leave the Republic of Ireland or leave and come back again. You may find more information on the official link: http://www.inis.gov.ie/en/INIS/Pages/Re-entry+visas.
The On-Line Appointments service for customers seeking Re-entry Visas from Re-entry Division, Irish Naturalisation and Immigration Service will cease as and from the Monday, 3 September, 2018 with the exception of emergency re-entry visa on-line appointments. All applications for re-entry visas will now be received through the registered post postal system. Customers are advised to submit their postal applications 5 to 6 weeks prior to travel.
yWith the appointment, you should receive the visa on the day of your appointment when you pass the application. It always processes in the morning so all appointments are in the morning.