On weekdays, I drink it when I get home from work and before dinner. It helps me transition from Work Brain (get things done, tie loose ends, be on top of stuff) to home life (be open to my family, debrief from the day's pains and triumphs, talk about the future) and it works really well that way.
On the weekend, sometimes I have some in the afternoon, but generally I start to get a little sleepy and nap before evening time.
In terms of frequency (another part of your question) I drink it every other day, roughly, and I find that next days are often much lower anxiety than they'd be without kava the day before. The "hangover" effect is something that I count on to even me out and not get too caught up in reactive bullshit.