According to flightstats.com (SN) Brussels Airlines 2640 Flight Event Timeline
Code:
Time
Date UTC HAJ BRU Event Data Updated
May 5 03:22 5:22 AM 5:22 AM Time Adjustment Estimated Gate Arrival Changed To 05/05/16 01:15 PM
May 5 03:58 5:58 AM 5:58 AM Time Adjustment Estimated Gate Departure Changed To 05/05/16 12:00 PM
so they had already changed the departure and arrival times when the OP saw the plane was sitting untouched at 5:30am. The estimated gate departure time was later changed from 05/05/16 12:00 pm To 05/05/16 01:30 pm and the flight eventually left the gate at 01:35pm.
As others have said there was no reason for someone to be working on the aircraft until spare parts or a mechanic arrived.