Well I always used my 501 calibrated delay and wanted delay of 639. This always, always worked for me, and I could hit my seed in 5 minutes.
Now, I have a 481 calibrated delay, and my wanted delay is still 639, but I never hit my seed anymore. Maybe I'll just try setting Pikatimer to a 501 delay and see if I hit my seed again.
If you aren't hitting it with a 481 calibrated delay, what makes you think it is 481?