How would I stop a while loop after n amount of time?

how would I stop a while loop after 20 seconds if it does not achieve what I want it to achieve.

like this:

from interruptingcow import timeout
try:
    with timeout(60*5, exception=RuntimeError):
        while True:
except RuntimeError:
    pass

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My Code is as Follows:
while not exists(A.png): #A.png=9999
    mouseMove(B.png) #B.png=PLUS
    mouseDown(Button.LEFT)
else:
    print("check!")
mouseUp()

p.s. I want to add from 0 until 9999, and don't want use click instead mouseDown,
hope someone can help me, thanks.