This
While I agree that our warming is contributed to warmer overnight lows there is actually strong influence by a warming ocean on this. If you think about it, a warmer ocean yields greater low-level moisture. This is one reason why I think we've seen an increase in cool season severe events (especially closer to the coast) the past several years. The warmer waters are yielding greater low-level moisture which in turn is yielding greater low-level instability.
And with the warmer oceans and higher concentration of low-level moisture you're decreasing the efficiency of radiation. H20 is a stronger heat trapping gas than CO2.
But yeah...this process will have a much stronger influence on nighttime as opposed to daytime. This is because H20/CO2 does not absorb shortwave radiation emitted by the Sun that well, but they do absorb longwave radiation emitted by the Earth very well. (Note: I know CO2 does...not sure if this is true for H20 as well. Don't remember).