when does the look-back-rule go into effect after a hit batter

[Dakota]

For the benefit of the OP (since you know all of this)..

There are overly complicated (IMO) and even goofy (IMO) rules for the LBR when the BR overruns 1B. (ASA 8-7-T-3 b thru e; NFHS 8-7-4 b thru e) If the BR overruns, she can find herself in a situation where she has not yet stopped, but is nonetheless committed to either 1B or 2B, no option.

None of those overrunning rules apply when the BR rounds 1B. The rule for a BR who rounds is ASA 8-7-T-3a / NFHS 8-7-4a. If she rounds, she is not committed to either base until she stops and then moves again (assuming F1 has the ball in the circle and is not making a play). She is allowed this stop, and rounding 1B and continuing toward 2B does NOT commit her to 2B. She may still take her one stop and then return to 1B, if she so chooses.

If she stops ON the base (and F1 has the ball in the circle and is not making a play), she may not leave.