Web Service slow on first call of the day

(cross-posting to MIDRANGE-L)
I have developed a web service with the Integrated Web Services facility (IWS) that is almost production ready, but I'm noticing that the very first call of the day takes 30-45 seconds to return a response. A subsequent calls provide sub-second responses, and that continues throughout the day. I'm normally pretty patient, but this will be used to provide data to a customer-facing web site, and if I was the first customer of the day to the web site, I'd give up if it hung for more than 10 seconds -- by 30 seconds I'd be off doing other things for sure.

My questions are:
1. What are the likely causes for the delay-on-first-call behavior?
2. What might I do to either eliminate the problem, or perhaps simulate a call on web server start-up, so that the first customer gets an acceptable response time?

In our environment, we take down most subsystems overnight, for database back-ups, for about 2 hours. When that completes, a n orderly CL-driven start-up occurs, and the various subsystems are restarted and are ready for action by about 4:30 AM. The web services are automatically active as the web server comes up.

The web service itself calls an ILE-RPG program that calls a number of service program procedures to gather data elements needed for the web site presentation and navigation. Most of those procedures use embedded static SQL. In my testing, I use the SOAPUI utility to simulate the calls that the web site script would use, and it is with the SOAPUI calls that I observe the delay in response on that first call.
My guess is that at least one component along the way takes a long time to set up open data paths or something else that all the subsequent calls get a free ride on, but I don't know enough about what goes on behind the IWS curtain to know if there isn't an obstacle there.

All ideas are welcome. Let me know what other details might be helpful.
Thanks!

Michael Koester
Programmer/Analyst

DataEast