Zanarkand-> Besaid 1 day

Besaid->Kilika 1 day

Kilika->boat to luca 1 day

Boat to Luca ->Mi'ihen high road 1 day

There's another night somewhere after Operation Mi'ihen, so at least one day, probably more than that.

Then we don't see another nighttime/twilight scene until The Spring (that I can remember) so that's another at least one day, probably two or three..

From there to Zanarkand is the same case, so another one and or two days.

Minimum of one week, based off of in-game sunsets and twilights.