For OTA digital signals it is likely that all the channels that you watch will come from several different multiplexes (Mux) each on a separate frequency, this is how it works in the UK anyway. When switching between channels on the same Mux the change will normally be slightly faster than when switching between channels on different Muxes. This is because the tuner has to switch between frequencies to change channels and hence incurs the extra time cost of doing that. I do know someone who started off putting their channels in order of the multiplex that broadcast it (with the shopping/rubbish channels deleted) so that it was quicker to change channel. They found that annoying though and just used their own channel numbering scheme afterwards.