Hi there my friend,
The amount of time to reach SP actually varies from person to person. Some may reach the SP phase in a matter of seconds while others have to wait for a surprising 30 minutes. I kind of agree with Din's answer, the main thing about WILDing is to sleep, but be mentally conscious throughout the whole process. So you see here that the method needs patience, mastery of the method and a good amount of luck. But don't be downed, have you tried WBTB(wake back to bed) before attempting to WILD? Combining WBTB and WILD makes WILDing much more easier to perform. Hope this helps and good luck in WILDing