tidal forces - When did the Moon stop?

"Protection" isn't the only effect of Earth. Here is a different POV: Earth may have accelerated impactors by gravity assist.

A different approch is the thinner crust, as suggested for the near side, which may have allowed asteroids to penetrate Moon's crust, such that lava could flow into the basins, or which may have favoured volcanism on the near side (see "Lunar interior" on this site).

A third approach is the protective property of Earth preventing the near side to be covered with many new craters, hence leave the maria visible.

According to Wikipedia the time to lock tidally is about
$$t_{mbox{lock}}=frac{wa^6IQ}{3G{m_p}^2k_2R^5},$$
with $$I=0.4m_sR^2.$$
For Moon $k_2/Q = 0.0011$, hence
$$t_{mbox{lock,Moon}}=121frac{wa^6m_s}{G{m_p}^2R^3}.$$
With Earth's mass $m_p=5.97219cdot 10^{24}mbox{ kg}$, Moon's mass $m_s=7.3477cdot 10^{22}mbox{ kg}$, Moon's mean radius of $R=1737.10mbox{ km}$, $G=6.672cdot 10^{-11}frac{mbox{Nm}^2}{mbox{kg}^2}$we get
$$t_{mbox{lock,Moon}}=121frac{wa^67.3477cdot 10^{22}mbox{ kg}}{6.672cdot 10^{-11}frac{mbox{Nm}^2}{mbox{kg}^2}cdot{(5.97219cdot 10^{24}mbox{ kg})}^2(1737.10mbox{ km})^3},$$
or
$$t_{mbox{lock,Moon}}=7.12753cdot 10^{-25}wa^6 frac{mbox{kg}}{mbox{Nm}^2 mbox{km}^3}.$$
Parameters are $w$ the spin rate in radians per second, and $a$ the semi-major axis of the moon orbit.

If we take the the current simi-major axis of the moon orbit of 384399 km
and a maximum possible spin rate of
$$w=v/(2pi R)=frac{2.38 mbox{ km}/mbox{s}}{2picdot 1737.10mbox{ km}}=frac{1}{4586 mbox{ s}},$$
with $v=2.38 mbox{ km}/mbox{s}$, Moon's escape velocity, 1737.1 km Moon's radius,
we get
$$t_{mbox{lock,Moon}}=7.12753cdot 10^{-25}cdot frac{1}{4586 mbox{ s}}cdot (384399mbox{ km})^6 frac{mbox{kg}}{mbox{Nm}^2 mbox{km}^3}\
=501416mbox{ s}^{-1}cdot mbox{ km}^6 frac{mbox{kg}}{mbox{Nm}^2 mbox{km}^3}=
5.01416cdot 10^{14} mbox{ s}.$$
That's about 16 million years, as an upper bound.

If we assume a higher Love number for the early moon, or slower initial rotation, the time may have been shorter.

The time for getting locked is very sensitive to the distance Earth-Moon (6th power). Hence if tidal locking occurred closer to Earth, the time will have been shorter, too. That's likely, because Moon is spiraling away from Earth.