How do I format a date field (@scheduledStartTime) in AWS?

I'm trying to grab the past hour based on the @scheduledStartTime field in AWS, but am having difficulty. The following works for grabbing just the current hour: hh=#{format(@scheduledStartTime,'hh')} which returns something along the lines of hh=06

I've tried this hh=(#{format(@scheduledStartTime,'hh')}-1) which returns hh=(06-1) when I actually want hh=05

How do I properly subtract the 1 from the field so that I get hh=05?