Depends on your hemacrit, hemoglobin, RBC. Did you donate to lower your RBCs? If you did then it's immediate, start whenever. I've heard from a few friends that the rising RBC then donating routine can spiral out of control so be careful.
Outside of blood counts I wouldn't recommend donating just to "clean" your blood for a cycle. It takes up to 6 weeks to fully recover from giving blood and not being at peak performance is counter-productive for a host of reasons.
If you want to avoid being at reduced capacity, the first big recovery is at the 3 week mark. After that 5-6 weeks is full recovery, but a little FYI. Last time I gave blood I felt like **** for months! Lost minutes off my 5k run averages and it took months to get it back, not 6 weeks. I'm chalking it up to my age (nearing 40), because when I was younger I'd recover in weeks. All my bloods are normal so I'll donate again one day, could have been fluke.