It doesn't work that way. The east coast observes daylight time during a similar period in which the UK observes daylight (summer) time, meaning you can't convert between BST and EST, only BST and EDT. 7:30pm in BST is 5 hours ahead of EDT so it would be 2:30pm on the east coast
Of course there are exceptions such as a couple of weeks in March and October where the UK would be 6 hours ahead of the east coast
Of course there are exceptions such as a couple of weeks in March and October where the UK would be 6 hours ahead of the east coast