The question doesn't make sense. Are you asking how to power down? Or are you wanting to know when users should start powering down?

Codingdefined answered the first question. The power down converts 1/12 of your HP to HIVE each week. It takes 13 weeks (91 days) to completely power down.

After you power down you can transfer your funds to an exchange and sell it for local currency.

The catch here is that the exchanges charge transaction fees.

It is not worth powering down until you have a few hundred bucks in the account.

When should accounts power down is a more difficult question.

If you decided to leave the platform; then you should wait a week so that you collect all of your last rewards; then press the power down button and come back in 91 days to cash out.

You have both a HIVE account and a STEEM account. SteemIt just changed the cash out formula to 4 weeks.

You could power down your SteemIt account and get your money in 5 weeks. I looked, your SteemIt account is worth $8.18.

Since you don't need two accounts. I would chose one of the accounts. Power down and cash out. I would power up the other account and keep blogging until I had the cash from the first power down in hand.

If you want to stay on the platform; then it is a question of how much HIVE POWER you want in your account. Having HIVE POWER increases the size of your rewards. You only have 45 HP and 2.95 HBD. That is about the minimum amount that you need in an account for it to work well. Personally, I would power up and not consider powering down until the estimated account value was several hundred dollars.