There are no restrictions on selling the shares or buying more of any share you like. You can sell the shares at any time after redemption. 

Stake has a holding period during which the value of any gift cannot be withdrawn from your US brokerage account. We do this to protect unauthorised use on credit cards and also to protect Stake from fraud.

The reason we do this is that to protect their users, card merchants permit card holders to submit claims for unauthorised use. To protect the customer and Stake against unauthorised use, Stake has a sixty (60) day holding period from the date the gift was redeemed. 

During this period, if you sell your shares, you need to wait until that 60 day period has lapsed before taking the money from your account.