How much time ca we rewrote a CD-RW disk ?

Depends on the disk.

I've redone some a dozen or so times and still going without a problem, I've redone others twice and then they turned into coasters. Differnet makers use different dyes. Some can handle more burns, others handle fewer. Go with a well known brand, and hope for the best. I've had little trouble with Maxell and TDK. I've had mixed results with Sony's disks (Weird... You'd think that the outfit that invented the technology would be able to make consistently good media) I've had an off-brand spindle of 50 burn a total of 3 coasters so far... "Ya pays yer nickel, ya takes yer shot"