Yes, well it sounds like you are pretty expert yourself. So you know that all that douching really isn't advised. I would say read a book on anal sex by Morrin- and you will have all the answers you really need to know. As far as I know , there is no specically good time in the day- but of course, you are likely to have less fecal material if you have eaten early, defecated, and not eaten again before sex. Having anal sex before dinner might be one thing you can try.
But I really would stop douching so often. You may rob your colon area of the ability to fight off other kinds of bacteria- and you don't want to do that. You can enjoy anal sex in a monogamous relationship=just make sure you are well lubricated and watch those finger nails- you don't want any fissures or scratches for bacteria to get into. If you are worried about fecal material, use a well lubricated condom- that's the safest approach anyhow- and can make your sex more worry free.
If you want an expert's perspective, read Anal Pleasure and Health, by Jack Morin, The Ultimate Guide to Anal Sex for Women, by Tristan Taormino, and the Ultimate Guide to Anal Sex for Men, by Bill Brent. The first is probably the most scientifically-oriented and well researched, but all three are excellent.