No they don't. The gate close time they give is usually the time the gate opens. That said I'd try to be there within 5 or 10 minutes of the gate close time they give.
No problem with time in my view ... if your flight is at 10:50 then the aircraft to operate it will only be due into Cork around 10.10 ... so at best they'll be starting boarding around 10.30 so you'd want to be at the gate not that long after that.
The gate close time is usually a work of fiction .. the main exception I find to this where you sometimes need to be careful is on early morning flights where it's the first flight of the day for the aircraft so they often try to get it boarded up and away early (and security can be busier at that time of the day as well)