SQL多行到列的性能非常慢

I'm having serious performance problems with a particular SQL row-to-column translation. A single query takes up to a minute to pull up 6 hours of data. I've simplified the tables below for clarity, but there's well over a million datapoints per day so the table size might be contributing. I don't have much experience with complex queries like this so I'd like some advice. The data tables are as follows...I'm having serious performance problems with a