I am a new gardener too. But. I think its ok to plant even now as long as you water regularly. If you plant in fall, they may not have enough time to get established before the ground freezes. I would water them biweekly until fall and then slow down to see how they are doing. Lets see what other gardening experts say about it.

Good question frida. I've always gone by the eventual size of the plant and roots. Like flowers should be ok after a season, but trees may take 2-3 years, depending on how big they were when they were planted. The bigger they are, the slower they will recover from the shock of being transplanted. I try to plant trees and shrubs as small as I can find so they will suffer less and take less time to recover.

. . . when you yank on them & they don't come up ;)

Frida, I had rather large trees(red oak)planted last fall, but was told I could wait until early spring~~I was TOO anxious to wait! I watered every 5 days, less when the rain came. I'm now back to watering every 5 days.

I just had more large trees planted and was told the same thing, every 5 days. They're mulched quite well to retain as much moisture as possible1~as the mulch breaks down, i'll add more. I think the secret to planting in Texas is not to let the soil EVER dry out until the plant seems to be securely established, which could be longer for larger trees, etc.

I won't be doing any yanking! LOL

Drip watering for long periods of time is best for trees.
The water goes deep and causes the roots to follow it.

Waiting until fall is an excellent idea, because the plants have all winter to get roots established. Plan things, get your hardscape in, install drip and wait until September.

I establish drought tolerant plants in Phoenix summers with this schedule, increasing the quantity as I decrease the frequency.

Plants: Before you plant them (except for conifers) prune 30-50% of their top foliage off. This minimizes the load on the roots for the first few weeks.

Planting holes: Fill with water and let it drain, then plant and backfill the hole with native dirt, fill with water again.

When you water, water thoroughly. Use a moisture meter instead of guessing. I have very sandy silty dirt, not Texas gumbo.

Daily watering for the first week to get them over the root damage.

Every other day for the next two weeks, or until I see them starting new leaves, whichever comes later. You will see them looking perkier in the afternoons.

Twice a week through the rest of their first summer, unless the moisture meter says otherwise.

Once every couple of weeks (if needed for that species) for their first winter)

Twice a month thorough soakings after their first winter, unless they are looking stressed, until they are close to the size I want, then whatever adults need. Usually a thorough soaking in late May gets then through to the summer rains.

In my opinion, fall is much much better. Our ground doesn't freeze, and fall and winter is our wet time. The plants will have a bunch of months to settle in and grow some roots before our horrendous summers start. If you plant in the fall, you won't have to water weekly for an entire year, just water when the plants look stressed.
As far as how long till they are established- I've had some plants that I watered when I planted them and never watered a 2nd time and they did just fine. Other plants need water throughout the summer and will show you that very dramatically by wilting. Some plants will croak if you water them too much (especially the drought tollerant ones). Others will croak because they don't like Texas heat (this seems to apply to most everything they sell at the big box stores). What I'm saying is that it's all up to the plants, just watch them and water appropriately and they'll be fine.