Belfast to Dublin - Sat or early Sun?

I just finished this trip. Our guide suggested you take the bus 5 hours before your flight departure time. There are two buses (Aircoach and Dublin Express) and he suggested buying the bus ticket a week or so in advance. Most of the people on my tour took the bus to the airport on Saturday. The bus stop is a short walk from the Europa Hotel.

I spent my final night in Dublin and took the train from Belfast to Dublin Connolly station.

I think this is really personal preference. Do you want to spend 2 hours on the bus before your flight or do you want to spend your last night closer to the airport?

If you are flying directly to the US from Dublin you will pre clear US immigration at the Dublin airport. That means you should be at the airport 3 hours before your departure.

Why is it that everyone a!ways denies the existence of the Translink service from Belfast to Dublin airport?
Translink are the state operator of Northern Ireland.
The original operator long before these other internet competitors.
At Belfast they leave from Grand Central Bus Station as opposed to a street side stop. They are also the cheapest option.

You might want to consider spending the day in Belfast, enjoying an early dinner, and then traveling by bus to the airport area. We just returned from Ireland and spent our last night at the Premier Inn near the airport (shuttle runs directly to the airport every 30 minutes around the clock). It was clean, comfortable, and relatively inexpensive — perfect when all we needed was a place to sleep before a morning flight. Your travel day is going to be exhausting as is — do you really want to add getting to a bus and the drive to the airport to a long day at the airport and on a plane?