Your field construction is wrong. It should be:
{ if { MERGEFIELD r2_srl }<> "" "{MERGEFIELD r2_srl \@ "h:mm"}-{MERGEFIELD r2_sru \@ "h:mm"}P"}

My own preference would be:
{IF{MERGEFIELD r2_srl}<> "" "{MERGEFIELD r2_srl \@ "hh:mm AM/PM"}-{MERGEFIELD r2_sru \@ "hh:mm AM/PM"}"}
so the AM/PM display is correctly set by the fields themselves.

__________________
Cheers,
Paul Edstein
[Fmr MS MVP - Word]