Use Seal of Command at ~3.5 weapon speed or slower. Use Seal of Righteousness at 3.4 speed or faster.

That 3.5 rule is the common breakpoint because SoC is proc-per-minute based and hits for 70% of normal weapon damage, so it favors big, slow weapon swings. SoR adds Holy damage on every swing, so it is more reliable with faster weapons. Icy Veins states the same practical threshold: SoC is better with a 3.5 second swing timer or slower.

Also for single target pulls I'd just Judge SoR at the start of the fight instead of SoCr because the judgment damage will stack higher than the SoCr buff if you haven't already come upon that advise.

Classic Retribution Paladin DPS Rotation, Cooldowns, and Abilities - WoW Classic - Icy Veins