People ask for a speed, but a speed is a promise, and a promise needs a source.
The sources give no timetable
A quoted rate of progression is only as good as the origin behind it. Treat any page that gives you one without naming where it came from with caution. What is documented is a direction of change in the disc, not a clock.
What changes in the disc
OrthoInfo (AAOS) says that as people age, the water content in the disks decreases and the disks become less flexible. Wikipedia says normal downward forces cause the affected disc to lose height, and the distance between vertebrae is reduced.
Neither passage tells you how quickly this happens in one person. Both describe the mechanism, and the pace is a question for the clinician who examines you. For general background, the OrthoInfo sciatica page and the WebMD pain management center are places to continue reading.
Questions to take to a Little Falls appointment
Ask how your clinician will track change over time, and how often. Ask what each follow-up costs and whether the plan has a fixed term. A plan that needs frequent visits for years is a different commitment from one that reviews you once or twice, so get the fee schedule and agreement terms before you agree.
Comparing long-term care options
The American Academy of Pain Medicine is a professional body you can use to see how pain care is described. The Cleveland Clinic page on pain management is another general reference. Use both to build your question list, not to decide for you.
A practitioner's note
How fast your own discs change is something a clinician can track with you over time. Ask for a monitoring plan you can afford to keep, because a plan you drop after three months tells you little. Our comparisons stop short of medical advice.