If I could just chip in - didn't they mention 2 different communication times in different TOS episodes? In BOT it was several hours, but later (I forget which episode) it was 3 weeks! Is this the result of a destroyed subspace relay (small empire scenario) or a much larger neutral zone?
You are thinking of "The Enterprise Incident" when Sub-Commander Tal replied to Kirk's threat of calling for assistance that it would take 3 weeks until a message could reach Starfleet.
Could be that the Romulan "space bubble" had extended between "Balance of Terror" and "The Enterprise Incident" (thanks to warp drive?), that the Enterprise
made a call from the far side of the Romulan Empire or else.
It's also interesting that "suddenly" the Romulans are very well aware of Starfleet's personnel, but that could be information they gathered from the Klingon Empire.
I can't help but wonder what the Klingons got in return from the Romulans (probably the cloaking device, but apparently that did them no good in TMP
The whole concept of Earth outposts on asteroids, rather than space stations, seems to suggest - given our solar System - that the Earth outposts revolve naturally around the Romulan Star. Apparently they had no propulsion system of their own to even attempt evasion maneuvers.