Honestly, I haven't tried to give away Hive accounts yet, I can't confirm it. On the site there is the Help section where you can ask any doubts.
On the 91st day you will no longer have delegated Hive Power so there will be no Power Down period
If you buy Hive Power for 90 days, nothing comes back. You pay 1 BTC for a certain amount of HP delegated for 90 days. During this period your grades will be higher and you will have more Hives as a reward for your curation. After 90 days, you will no longer have HP delegated
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