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Although it will not necessarily harm the plant, most types of fountain grass do not require regular watering with exception to periods of drought. I’d say that in your particular area and for your circumstances, however, it is probably worth the effort to continue what you’re doing.

The ocotillo is also a drought tolerant plant and too much water can lead to root rot.

You need some patience with this warm-season grass. It usually takes a little while before you begin seeing signs of life, which should happen in late spring/early summer

This cold has damaged many plants this year, so it is possible that they did not make it due to the unusual cold. This article will help you determine if they are dead or not: https://www.gardeningknowhow.com/plant-problems/environmental/how-to-tell-if-a-plant-is-dead-and-how-to-recover-an-almost-dead-plant.htm

I would give them another 2 weeks, but if you do not see anything by then, they are likely dead. For future reference, it is best to leave the foliage throughout winter, as it helps protect the plant from too much damage. Pruning should be done right after winter to alloe for new growth.

Other than planting them in containers that you will then bring into a sheltered place, like a garage, in the winter, they cannot survive there through the winter. They should grow beautifully for the summer. If you do not want a plant that will die, I would just take them back. Home Depot has a very broad return policy and will not mind if you bring them back.

Yes, this plant is a perennial, if you live in a zone where it is hardy. They can survive in the ground and come back as long as it does not get colder than 20 degrees F. However, it sometimes takes a while before it comes out of dormancy, which should happen sometime in late spring to early summer.

They are only hardy down to 20 degrees F. It is likely that your area is too cold for them.