Inductive effect and bond strength
Just as hyperconjugation stabilizes carbocations and radicals by sharing the electron density of adjacent $\ce{C-H}$ bonds with the unoccupied/partially occupied orbital, hyperconjugation destabilizes carbanions. So more substitution means less acidic and more ionizable. I had a hard time finding a single resource listing bond lengths, but they seem to correlate with bond-dissociation energy. The wikipedia page for methane states that its $\ce{C-H}$ bond length is 108.7 pm and an answer by Jan says ethane’s is 109.4 pm.

$$ \small
\begin{array}{lcc}
\hline
\text{Hydrocarbon} &amp; \mathrm{p}K_\mathrm{a} ^{[1]} &amp; \text{BDE (kcal)}^{[2]}\\
\hline
\ce{CH3-H} &amp; 48 &amp; 104\\
\ce{CH3CH2-H} &amp; - &amp; 98\\
\ce{(CH3)2CH-H} &amp; 51 &amp;  95\\
\ce{(CH3)3C-H} &amp; 53 &amp; 93\\
\hline
\end{array}
$$



 $[1]$  Evan’s pKa Table
$[2]$ Wikipedia: Carbon-Hydrogen Bond