Is there a difference in the definition of a calendar day and stream day?

In general stream days are the unit the use before you include any PE or shutdowns. It is a streaming day with normal production. For constraints, you always use stream day, because a constraint needs to be constraining not for the average calendar day rate for the month, you need it for each specific day when you have full production. 

Uptime or PE multiplied by number of days for the relevant month will give the on-stream days.