There is no clear clarification yet since DO has not yet implemented the over charging for bandwidth after you cross the allocated limit.

Usually the bandwidth is tied up with monthly billing cycle hence even if you spin your droplet on 25th of a month, you will get fresh 1TB allocation from 1st again with new billing cycle.

But till DO starts their extra bandwidth charging rule, we don’t have to worry about this.

I also would like the answer to this. If it’s 1TB/31 then that gives you only 30G on the first day to set up your new instance but if it’s 1TB per instance then you could “cheat” the system by destroying and rebuilding your instance if you got close to your limit.