Most likely that no damage has been done. If the front derailleur (FD) was forced very hard it is conceivable that some damage could occur, but it is unlikely. Also, the six-hour time duration should not play a part in any relative damage that may have occurred. It is the movement that has the possibility of harming the system, not the residence time in that position.
The damage that "could" have occurred in theory is:
The FD cage could be "bent" some. Remedy: this can usually be un-bent. FD cages are pretty durable however, so unlikely. If a FD cage is bent enough, it may be difficult to restore the shape enough to restore shifting performance. But again, you would definitely notice if the FD was bent visually and by poor shifting performance.
The chain has been bent/deformed. Also highly unlikely, but the remedy would be replacing the chain if this happened.
The FD moved and the alignment adjustment was affected. If the attachment point(s) slipped due to the extra forces, then the alignment adjustment could be lost. The remedy would be to reset the adjustment and ensure that the attachment points are tightened correctly to the appropriate torque.
The cable on the FD slipped/lost adjustment. If the force is significant AND the bolt holding the cable to the FD was not tight enough, the cable could slip, which would affect the shifting and would be readily noticeable when shifting. Shift performance would suffer and it just would not work, or the chain would rub at times when it previously would not. Remedy: adjust the cable. Replace and adjust the cable if the cable was damaged (unlikely, unless it was ready to fail already).
Try riding your bike and see how the FD shifts now. If you do not notice any difference in shifting performance from what you previously experienced, you are probably fine, and no further worry is necessary.