Advise on setting

Hi,

I’ve installed W3 Total cache (free version) and sometimes pages are fast, then after a while they are slow again. I’ve set most of the W3 Total cache to expire after 24 hours, some settings more sensitive to changes to an hour.
I’ve installed Warm cache, but it’s not working 100% to keep all pages fast all the time. We have a sitemap with 624 urls total. The warm cache runs 30 pages every 30 minutes, however, the pages aren’t always up to speed. Can someone advise me on better settings? Thank you.