For the 60 minute frequency between Inverness and Tain, with some increases to 30 minutes between Inverness and Dingwall (both short workings and also the Kyle of Lochalsh trains for this section), ideally the track needs to be reinstated at Lentran to create a dynamic loop and also ideally, a dynamic loop somewhere between Evanton and Alness or Alness and Invergorden as it is an arrow straight section of track.
Without dynamic loops, the timetable would not be robust enough leading to delays and cancellations, which in turn would not encourage people to leave cars at home and use public transport.
The journey time Inverness - Muir of Ord (passing loop) is 20 minutes, Muir of Ord - Dingwall is 10-11 minutes totalling 30-31 minutes for that section. Dingwall - Invergordon is 17 minutes, and Invergordon - Tain is 19 minutes. In total, Inverness - Tain is broadly 63 minutes, and trying to build the timetable around the existing passing points can be challenging. I did start a thread in the Speculative Ideas section a while ago regarding a Taktplan (clock face departures) with 2 different versions. The second version was based on a hypothetical rail crossing of the Dornoch Firth, diverging near the caravan site north of Tain, crossing the Firth, into Dornoch, then the former alignment via Embo to rejoin the original route with a north to east curve towards Golspie.