Any time is a good time to PowerUp, but the best time is on PowerUp Day (P.U.D.) which takes place on the first day of each month. Eligible participants vie to win prizes of delegations and tokens. The concept of PUD was conceived by 
The official post about the 01-Jul-2020 HivePUD can be found here, and it contains requirements for eligibility as well as prizes:
@traciyork/announcement-post-hive-power-up-day-july-1st-2020
Not long ago, someone asked what it means to "PowerUp" so I explained it this way:
To "stake" a token or coin means to invest it, to prove your interest in the future of it. The HIVE you earn can be "staked" as a sign that you believe in the future success of the blockchain, and to signal your intent to keep the earnings there for some time. In exchange, those who have staked HIVE will receive dividend rewards on the stake from time-to-time, just as stockholders earn dividends periodically. Those who stake HIVE into Hive Power (HP) also are rewarded with more influence in the form of additional Resource Credits (RC) for processing transactions, greater value on upvotes and curation rewards, and more weight in stake-based matters in the DPOS environment.
I have participated in PUD before, but am no longer eligible for prizes because my total HivePower (HP) is greater than 8,000. But, that doesn't mean that I am not PoweringUp this month — because I did! The following screenshots from my Hive Wallet show the 'before' and 'after' views!
BEFORE:
AFTER:
≈✿≈ Did you PowerUp today? ≈✿≈
😊
to learn more about either of these projects, please visit: 
01-Jul-2020