is there a period of acceleration for light at the start?

Nope.

But I wonder what's going on within the Planck length of that first 10 ^-43 seconds of the quantum leap?

What?????

All space-time and gravity lose their classical definitions within the tiny fractional units of space-time, and quantum effects take over. Space, matter, electromagnetic waves, and gravity, are not continuous....if you roll a particle toward a wall, it will 'jump' that last 1.6*10^-33 centimeters without passing through space or time as we know it. This is what I call the 'quantum leap' through the 'secret of the zero'.See here Planck Time

100 years have passed from the date of creation of SRT.
Millions of articles, reviews and books have been written and the
United Nations has decided to establish 2005 as the centennial year of SRT.
Considering all that is clear in this theory, one must still
continue to be surprised by its unusual aspects
Lets review it again:
1. SRT is based on two postulates:
a) According to classical mechanics, physical processes,
which occur in rest or in a rectilinearly driven reference system
are described under the same laws.
b) The rectilinear - uniform propagation of a quantum of light (c=1) in vacuo
has a constant magnitude and does not depend on the source of radiation.
These two postulates would be proven if in the final analysis, they corresponded
with Galilean transformations. However, the result appears negative.
Galilean transformations do not unite these two theories. Why?
2. The rectilinear - uniform motion of a quantum of light (c=1) is connected with
Maxwell's classical electrodynamics. SRT has grown from Maxwell's electrodynamics
and main component in it is the electron.
What describes the electron in Maxwell's electrodynamics?
It is natural, that this electron should be in motion, but it does not move rectilinearly.
It rotates around its own diameter ( spin of Goudsmit-Uhlenbeck)
and such a rotation creates electrical waves. In such rotation all geometrical
and physical parameters of the electron are changed.
It is for this reason Einstein utilized the Lorentz transformations.
And all that is sensible in SRT is that it examines two completely
different types of movement: rectilinear (quantum of light c=1)
and rotational (Maxwell's electron).
It examines the transformation of the electron into a quantum of light (photon)
or quantum of light into an electron .
3. According to classical electrodynamics, an electron in rectilinear motion
does not create electrical waves. Why?
Because the electron travels as a quantum of light (c=1).
In such movement its geometrical form is a circle.
In such movement its area of contact with the vacuum is minimal
and it is not capable of changing the uniformity of the vacuum.
4. When the electron rotates around its own diameter, its speed is more
than the rectilinear motion of a quantum of light. Its speed is c > 1.
For this reason physicists ascribe a huge frequency
to the electron which is the reason its energy E =ħw is higher.