This difference in estimated time vs actual time is inherent to 3D printing and gcode.
When slicing a model with specific speeds in a profile, a gcode is generated with speed parameters, ie G1 X1 Y2 E3 F3600 tuned to those speeds. The F parameter, is speed in mm/min and can be seen as a “print speed wish”, in a sense that it will instruct the machine to execute at that speed. The firmware of the machine reads this speed indication, but has it’s own limitations in acceleration and in maximal speed(amongst other limitations). As where a gcode could instruct the machine to go F6000, a machine itself could limit the speed by a big margin because it just can not accelerate that fast or it’s max speed is limited.
A slicing software like Simplify3D estimates it’s print time based on the speed setting, but if a printer can’t execute it at that speed it will take longer. Simplify3D also does not take into account any accelerations or decelerations settings of the printer, which are different for each type of printer, hence even more difference in estimated time. The Xeed has quite low acceleration because of it’s sturdy head design, which will result in that it will not hit the indicated speed by the gcode, especially in smaller prints.