Our lab uses in situ PCR slides from Perkin Elmer.  We heat the slides with
the tissues (paraffin, 5um)to 60C for anywhere from 1-5 hours depending on
the tissue type.  We use the Perkin Elmer kit for in situ PCR, the buffer at
2x concentration, and a pro K digestion that varies in concentration and
incubation time depending on the tisse.  Obviously there's a lot of
optimizing going on here.  I hope this info is helpful.