This is one solution which prevents the timer from ticking.  Many other solutions are possible!

First, move the stone for the orange beam to reflect it home.
Step #1

Next, move the extra stone (near the orange beam) to one of the positions for the green beam.  Move either of the 2 stones reflecting only the green beam to reflect it home.
Step #2

Move the extra stone to reflect the white beam home.
Step #3

Move the extra stone to reflect the blue beam home.
Step #4

Here's the key move to reflect off one of the previously placed stones:  Move the extra stone to a position where it will reflect the pink beam after bouncing off one of the stones used to reflect the blue beam.
Step #5

Pick up the top-most stone of the pink beam and place it anywhere out of the way.  As soon as it is placed, the pink beam will reflect home off the one placed in Step #5.
Step #6

Next, move the extra stone to the left position of the planned yellow beam angle.  Finally, move the stone that's refecting the yellow beam to it's new position to reflect the beam home.
Step #7

If you did it correctly, the timer will never begin to tick and you should have an extra stone left over!
Solution