H1b premium processing

Is premium processing available for COS from H4 to H1 for applications that are filed after Feb 19 ,2019? Or is it available only for applications filed before 21st Dec2018?

No, it is not available for COS from H4 to H1B yet.
Yes, only available for application filed before Dec 21, 2018. For more info check : H1B Premium Processing Open for Filings on or Before Dec 21,2018 - RedBus2US