Hi hegartype,
Estimating operation runtime is pretty tricky, as you can tell by both PixelCNC and Gsender estimations being way off from the real world runtime. The best we can suggest is to go into your CNC/CAM Settings under the Config menu and adjust the Rapid Speed and Rapid Accel settings to closer match your CNC setup. The rapids between feed commands tend to be what throws off runtime estimation the most because there are many variables at play that affect how fast the machine is actually able to move during each individual rapid, but if you can tune those two settings to more accurately match your machine the time estimation should be more accurate. Generally, the more rapids there are the farther off runtime estimation can be - particularly if those two settings are not tuned to match the machine that G-code will be running on.
Hope that helps! :]
- Charlie