Unfortunately it's not possible to do this within the app itself as far as I know, but you can see it in a shell. In the below example I want to see all the alarm manager entries for my package my.package.name. The "when" field in my case is as Unix timestamp, so I rewrite it to a normal datetime:

for x in $(dumpsys alarm | grep my.package.name | grep -o "[0-9]\{13\}" | grep -o "^[0-9]\{10\}"); do date -d @$x; done