How to do it so it works, since the failure modes are consistent.
Use audio you can almost already understand. If you are decoding meaning you cannot keep up. Slightly below your listening level, not above it.
Short clips, repeated. Thirty to sixty seconds, ten or fifteen times, rather than ten minutes once. The repetition is where the improvement is; the first pass is always bad.
No transcript on the first passes. Read it afterwards to check what you were mangling, then go back to audio only.
Stay at the delay. When you fall behind, do not stop and restart - jump back in. Stopping turns it into listen-and-repeat.
Do it out loud and at full volume. Mumbling defeats the point, since the whole exercise is training your mouth. This is why people do it while walking or driving rather than in a quiet office.
Record yourself once a week and compare against the original. Unpleasant, and it is the only way to hear the errors you cannot hear live. Your own recording from four weeks ago is the most useful feedback available to you and it costs nothing.
Ten or fifteen minutes a day is plenty. It is intense and people who try to do an hour stop within a week.