The current version of Bloodstained Commendations are going to remain purchasable until Thursday when Phase 3 launches. Make sure to buy any you want before then!
Note that if you are already Rank 5 and you use them today, you won’t rank up tomorrow as the level cap has not increased yet. Rank 5 characters should use them after maintenance tomorrow so that you get that honor for the following week’s reset on April 9.