Learn English – it’s live vs. it’s on live

Not for a long time yet.

By definition, yet as used here means:

4) at some future time; sooner or later

but it is not time specific. So you have to look for another term for the time frame, in your examples "a while" or "a long time", whatever they mean in context. yet just emphasizes that it hasn't happened yet. It does not really add anything pertinent in your example. I would leave it out -

Not for a long time.
Not for a while.
etc.

I suppose the dictionary definition of "exactly" that the other answer mentioned sort of works, but in this context, as a native speaker, I'd interpret "right" to mean "near." So if someone told me to get something that was "right by her desk" I'd look for it all around her desk and expect to find it close to the desk.

Edit: As I mentioned in the comments, "by my desk" already means near, so "right" is used as an intensifier. The reason I don't think that "exactly" works very well here is that the meaning of "exactly" is very precise, and the concept of "by" isn't something that can be pinned down with exact precision. However, here are some examples using something that can be pinned down with precision:

It is in the center of my desk.

If you said this to me, I'd expect to see "it" somewhere close to the center of your desk, but I'd look in a fairly big radius.

It is right in the center of my desk.

I would now expect it to be closer to the center of your desk, and I'd look in a smaller radius, but I would accept that there might be some variance from center.

It is exactly in the center of my desk.

If you said this, I'd expect that if I got out a tape measure and measured your desk, I'd find it in the exact center.

It might be helpful to point out that this meaning where right means "exactly" or "almost exactly" is mostly used to intensify expressions that describe location or time. Here is another example, using time, of a way "right" is used to mean "almost exactly." If I arrived three minutes late to a meeting, the following conversation could take place:

Me: Sorry, I'm late.
Other person: No, don't worry about it. You're right on time.

Now, obviously, I wasn't exactly on time. But the other person is saying I was close enough to exactly on time that it doesn't matter. Other people have said my answer is wrong because "right" doesn't mean "near." They have a good point, but I maintain that this sense of "right" is used specifically to intensify closeness (in location or time). For examples, these two sentences mean almost the same thing:

She is right beside me.
She is close beside me.

Will brings up an interesting argument in the comments that "right above" doesn't necessarily mean something is any closer to an object than just "above." However, if you are standing in a room, any ceiling light is "above" you, no matter where it is in the room. If you say it is "right above" you, it means you are standing directly under it. If you measured the distance between you and it, it would certainly be closer to you than it would be if it were across the room!

The word "right" has a lot of meanings and can be used as an adjective, adverb, or noun. But this is how you can interpret it when used to intensify an expression of location or time.