This is not a common practice for softwoods. The value of the product and defect prevented has to justify the cost of sealing.
It wasn't clear what you had in mind on timing. Endsealing needs to be done immediately after felling to be effective (or immedieately after any transverse cut is made) to be successful. The ends of lumber units are sometimes sprayed after trimming in the sawmill. If a few hours elapse the effectiveness goes down because checks have a chance to get started. If applied a day or three after cutting, the coating will not be very effective. There's some literature out there to support this and I could probably dig it up, but this is essentially what it says.
You might check with one of the coating companies, such as AnchorSeal, for more information on how to use the coatings.
By the way, most of these coatings are wax based and in the hardwood industry are left on (no trim in the sawmill) during kiln drying to prevent end checks. The wax melts at softwood temperatures making them less effective in the kiln.