I think you may be missing the point here.
The weak link is to protect the glider airframe from exceeding maximum
loading ie towards the top of the launch, with the cable almost vertical
and the wing loading at its maximum. Using these calculations to determine
the best acceleration at the start of the launch is bad math(s).
The acceleration on the ground should be safe. Too high and the inertia of
the stick and the pilot's hand will cause backward movement, with
self-evident results. Too slow and aileron authority is not achieved
quickly enough to prevent wing drop and possible cartwheel!
Typically aileron authority is present just below the stall speed so the
acceleration should be sufficient to get to that speed before a wing can
drop, say 2 seconds or so. Now do the math(s) for your glider. Typical
stall speeds are below 35 kt (17 metres per second). This gives an
acceleration of less than 1g which will comfortably be tolerated by any
pilot. If continued the acceleration will have the glider fully flying and
high enough to begin the rotation into full climb in another second or
two.
Broken weak links at the start of the ground run are generally due to a
snatched All Out. The launch marshal must ensure that there is no slack in
the cable before giving All Out by waiting for a genuine movement of the
glider. The wing tip holder must move forward with the glider for as long
as possible. The wing tip holder should abort the launch if he or she has
to hold the wings level, they should do so naturally or the wing will drop
on release.

Best wishes

JohnR-K