It also depends on how much tanins stained the water.. In heavily stained water purigen can get coffee brown in days time.
Now i'm not so sure about the recharging process with Bleach.. Since from a chemical view point bleach aint a solvent or absorbent. As cleaning agent it doesn't remove dirt it bleaches it hence its given this name. And every single professional cleaning company can tell you Bleach doesn't clean. it desinfects and it discolors stuff.
Than what does it do to purigen? My best guess it does what it does best it bleaches the grains light colored again but leaves most of the particals it absorbt untouched and in place. I kinda find it a suspisious product that has more question marks than effect.
I once bought a bag that claimed to be sufficient for a tank 4 times the size of mine. It was coffee brown within a week, cleaning it never made it white again and it was coffee brown again even sooner after cleaning. And it didn't realy have any visual effect on the tanks water color. It might be the cause that the tank contained over 7 kilo's Mopani wood as hardscape. That leaced like mad the first year. In my case nothing actualy did something vissible, carbon didn't and zeolite didn't. So i just waited it out with doing water changes.
Anyway, i have a strong feeling that purigen isn't recharged at all, it might just be able to take up quite a lot and a long time even without bleaching it. Bleaching might be a simple marketing story to give you the visual idea its doing something.
And if you have such little water staining so that you see effect. Than i think you might as well give zeolite a try.. That's a lot cheaper (if bought in the right place) and also can be recharged with salt water. In a way it kinda feels safer too.. I just don't like the tought of bleach comming close to my aqauriums, the idea gets even worse with soaking an absorbent in it that should be put back in the filter.
Can't help it i find Purigen a rather expensive fishy product. And Seachem is well known for keeping secrets.. Thus we can only take their word for it.. As with Easy Carbo, that contains 0 Carbo but it works..