Welcome to the folding@home support forum Perrygast!
artoar_11 brings up a very good point in his post below mine ... always give the estimates time to settle by waiting a few percentages. If that doesn't change your opinion then carry on with my post.
I'm fairly confident that your GTX 760 should be able to finish any of the current work units even though it is not running at night. I have a 660ti and although it's running 24/7 it would still finish on time if it were not running at night. My 660ti is averaging around 70,000 PPD. If it wasn't running at night I would expect it to still get more than the 11,666 that your screenshot is showing which leads me to believe the drivers might be the problem.
Two questions:
1. What drivers are you using? The later drivers are known to result in reduced performance on your model of GPU. I'm using 304.131 ... try a driver around that vintage if possible.
2. How many hours a day would you say your GPU is folding?
Also, there is a setting on the Config > Advanced page for Folding Core Priority ... you could try changing that from the default to Slightly higher.
To answer your question a safe way to remove a work unit is to right-click on the slot in FAHControl (aka Advanced Control) and select Pause, then go to Config and Slots ... highlight the slot (gpu in this case) and select Remove, OK and Save ... the Client should send a message back to the server that the work unit has been dumped and perform the necessary adjustments to it's status so that it will be assigned again. Dumping is not something we usually recommend but there are times when it can't be avoided. Personally, I don't think this is one of those times.