Why would I get a notification and email a out my stimulus check being received on my card today but says it won't be available till the 15th

I'm sure the funds needs to go through some steps before becoming available. 

Additionally, if your card was lost or stolen, this would give you a few days to request a replacement. 

From what I can glean it seems the IRS did some testing today to see if the new stimulus distribution system  is working  and  those payments  were not supposed to be released  until the 15th ... so now you know the funds are pending and when they will be released ...  you are one of the lucky ones so be happy. 

Glad I know. But theres other people in my household that already have the funds available. So I don't think it's a test.