Is your tank temp set to 24c, this is about your limit with the zebra danios being in your tank. When doing a fishless cycle the ideal temp is 29c, this seems to be the heat where bacterias colonise quicker. This certainly could be your reason for why things are taking a bit longer.I've been cycling since October 26th, 3 danios, and still nada on the nitrItes. Just FYI.
Hang on in there, skins.
P.S Can you post your next pH test results.