I have a lot of elbow bush around my place. This past fall I had about a 30 acre area cleared of cedars, brush etc.

It's spring and as expected the elbow bush is coming back. It looks like the best thing to do at this point is to treat stems with diesel/remedy but wait till mid July?

You can do diesel/remedy basal bark, year round. Obviously, it's easier in spring/summer when you have visible foliage (makes it easier to tell living from dead).

I've had good results with foliar spray of remedy as well (1-2% plus a surfactant). For that you'd want enough leaves to be able to be effective. Stuff that I've previously cut may take more than one application, but it's so much easier and cheaper than 20-25% in diesel that it's worth it, imo.
Honestly, I've found elbow brush to be relatively easy to kill, at least compared to mesquite, *****ly pear, tasajillo, etc.

For something like this, foliar is going to be your best bet. It's going to be multi-stemmed, which makes basal treatment almost impossible because you will miss some. I would wait until it's fully leafed out, as it's pushing up so much at the moment it makes it difficult for the herbicide to get down to the root system.