Is it possible to start a job at a set point during the burn? E.g. If I have a job that 50minutes long, can I start the job at the 30minute mark?
No, that feature is not currently available.
If the reason you’re asking is that you got halfway through an engraving and had to stop it, and want to continue it again, you can flip the Scan Angle value in the fill or image layer to 180 degrees, and it will run top to bottom, instead of bottom to top. When the new engraving meets the existing one, stop it.