Jaisalmer is the kind of place where the buildings do half the talking. Almost everything is cut from the same warm sandstone, so the whole old city seems to change color as the day moves along. I would plan around that light rather than around a long list of sights.
Start with the fort, not the clock
The fort sits high above the town, and its walls are worth walking slowly. Go early if you can, before the lanes fill up. Wear shoes you can walk in on uneven stone, and carry water and a hat. Opening times and entry rules change, so check the current details before you set out.
Look up in the old lanes
The carved balconies and windows of the havelis are easy to miss if you only watch your feet. Stop often and look up. Some of these buildings are still lived in, so keep your voice low and ask before photographing anyone.
Let the afternoon be quiet
Midday can be hot and bright. I like to rest then and return when the stone turns gold. A cool drink, a shaded seat and no schedule were the best parts of the day.
Stay for the evening glow
Fort walls look dramatic once the lights come on. If your plans allow it, end the day outside and watch the color deepen.
A slower day here is mostly about paying attention: the carving, the color and the people around you.