Maximum delay is unlimited really. However, RNGReporter has a limit of 9999, I think. So you want to look for seeds that are between 600 and 9999 for DPPt and 500 and 9999 for HGSS.
You can also change your wanted second to make Pikatimer run faster. So if your usual seconds are 16, but plugging 55 seconds into the wanted second makes the timer faster, you can use 55 seconds in the Seeds to Time window of RNGReporter. This is helpful if Pikatimer gives you a 1 minute countdown on the first time and another 1 minute countdown on the second one. Sometimes just changing the wanted second gives you a better set of countdowns so you can save time on your project.