I have been using IIS7.5 Since its release. I am also using commerce server 2007sp2. Due to Commerce Servers Need for memory and processor I have the app pool the website is assigned to recycling at midnight every night. My Question is what is the best time table to recycle heavy web app pools? I am looking to keep speed and not bump potential customers while recycling multiple times a day if possible. Another issue is that every few days the same app pool will hang and I have to force a reset of IIS to get it working again.
I think that it is hard to recommend any schedule for recycling since that really depends on the business side, for example, is your site primarily US-based or is it globally accessed as well? In general I would recommend looking at your analytics and determine when its "safer" to perform the recycling.
In fact the reason IIS uses 29 hours as the default was to have more of a "sliding" time, since having a default of 24 would make it always recycle at the same time and depending on when the apppool start that could be your "top" customer time and then you would be stuck for that every day.
So really there is not a good answer other than determine for example that if your customer base tends to be low at 2:00 am then use that. And of course if you enable specific schedule, make sure that the recycling interval is set to 0.
Whatever you choose make sure you do not disable Overlapped recycling (the default) and that way the downtime is minimal since IIS will continue serving requests while getting the new AppPool ready. If you are using IIS 7.5 you could even use the Application Warmup feature (still in Beta) to warm up the apppool before it starts handling requests, that way you never have a "slow" response.