Engine fire B737-300/900 QRH procedure

[downwind]

Hi All

Appreciate if I could get some opinions on this procedure..... Based on the B737 QRH....................

step 5

"If the engine fire switch or ENG OVERHEAT light is
illuminated:

Engine fire switch . . . . . Rotate to the stop and hold for 1 second
If after 30 seconds the engine fire switch or ENG OVERHEAT light stays illuminated:

Engine fire switch. . . . . . . .Rotate to the other stop and hold for 1 second

In the first instance when does the timing start for the 30 seconds then????.......

this is not clear in the QRH is this after confirmation of the fire bottle "DISCHARGE LIGHT has illuminated"???

thank you.