On the 731-3 powered aircraft I have flown, MGTOW long range cruise profiles at constant altitude and constant long range mach could generally be planned to follow this fuel burn schedule:
1st hour 900 lbs per engine
2nd- 750
3rd- 700
4th- 650
5th- 600
6th- 550
By flying a more agressive max range profile with step climbs from FL330 to FL410and diminishing mach speed, (constant AOA) about 50 lbs less per hour per engine would be consumed.
Normal cruise planning averages about 100 lbs per hour per engine higher than the figures listed above. The higher weight/thrust ratio of the fully loaded DA50 may push the fuel burn higher than these figures for a twinjet. So you could burn up 12,500 lbs of your full-up 15,000 lbs in anywhere from 5 to 6 1/2 hrs depending on the profile selected. This probably results in a maximum still air range of about 2,750nm at max LRC and about 2,200 nm at normal high speed cruise. If I am very far off, please let me know. Maybe it's the 900 that has the 3,500 nm range.
Best regards,
Westhawk