A319 Captain reported a rejected takeoff due to Integrated standby airspeed anomaly.

Narrative

We flew the aircraft from ZZZ1 to ZZZ and wrote up NAV ADR 3 and the airspeed indication on the ISIS (Integrated Standby Instrument System). A red SPD flag was showing over the indicated airspeed. ZZZ Maintenance reissued the MEL for the ADR3 fault which had been cleared the day before. With ISIS speed ZZZ Maintenance had to do some more extensive tests. After everything was signed off; we were within 40 minutes of MOT (Minimum Off Time). As we taxied out; we noticed some issues with the lower ECAM not showing the flight control page during the flight control check. After speaking with Maintenance Control; they advised a return to gate. ZZZ managed to reset a few things and the lower ECAM seemed to work. At this time our MOT had expired so we decided we could extend our MOT by 1 hour. We taxied out to the runway; completed the before takeoff checklist. This time the lower ECAM responded normally. We were cleared for takeoff and noticed the ISIS indicated airspeed did not move. As we passed 60 knots; I realized it was not going to work. I rejected the take just before 80 kts; and informed ATC. I feel I could have been more prompt to reject and not wait so long to call the reject. The auto brakes were quite aggressive at stopping the aircraft. After we exited the runway; I made a PA explaining what happened and returned to gate and shortly after timed out. I made 2 logbook entries for the ISIS and rejected takeoff. The FO did a walk around after we arrived at the gate and everything looked normal.Cause: The fact that I woke up at XA:45 in ZZZ2 for a XD:00 departure; I'm sure had something to do with my slow reaction to reject. Also the accumulation of events and a return to the gate also had an impact; specially so close to MOT.