No. The duration of Wish is instantaneous
In the quoted Sage Advice, "duration" refers to the the "Duration" field of the spell's description, not whether the spell has a lasting effect. Wish has a duration of Instantaneous; therefore, the spell is instantaneous, even though it has a lasting effect.
I realize the example you give involves an ongoing effect created by magic. When someone tries to dispel it an hour later, though, the catch is that the effect was created by magic. After it was created, the effect simply existed, without the aid of ongoing, dispellable magic.
As the Player's Handbook puts it:
A spell's duration is the length of time the spell persists...
Many spells are instantaneous. The spell harms, heals, creates, or alters a creature or an object in a way that can't
be dispelled, because its magic exists only for an instant (PHB p.
Compare this to Plant Growth. It can either cause plants to become overgrown or cause soil to become enriched for one year (depending on how you cast it). The spell's duration, though, is Instantaneous. It cannot be dispelled.
- The overgrown plants are simply overgrown. If you want them gone, get
- The enriched land is simply enriched. If you want it un-enriched,
wait a year. If you can't wait a year, you'll have to get creative. Magically-induced erosion could work, or you might let the land stay enriched but kill the plants and/or the farmers.
Also compare to Fireball, which can burn people and set things on fire. The spell is instantaneous; it cannot be dispelled.
- If it sets your sofa on fire, your sofa is now covered in nonmagical fire; use a fire extinguisher.
- If it injures your fighter, the burns are real, but there's no magical residue; use Cure Wounds.
The bottom line
It's tempting to look at a spell like Wish or Plant Growth and say that, because the effect has a duration, the spell must have a duration. This is not what the rules say, though.
Fireball has a duration: The magic happens instantaneously. Fireball's effects also have a duration: they last either permanently or until someone reverses them (with a fire extinguisher, with healing, etc.). According to the rules as written, the addition of a timer to the effect of Wish does NOT mean that the effect continues to be magical. Wish CANNOT be affected by Dispel Magic; there's no ongoing magic to dispel.