The whole process is a lot more complicated then I have explained. 3 mins seems quite reasonable for what it actually does in the end. I do have a question about the code you supplied. Specifically this part:

IF OBJECT_ID('tempdb..#AreaReadings') IS NULL CREATE TABLE #AreaReadings(col1 int)

So back to the main question, what happens if the temp table #AreaReadings is being used by one instance of the stored procedure while another instance tries to start and create it again, does it just give an error?