(For this piece, I’m using the Quantum Mechanix Map of the Twelve Colonies — which we use for our Battlestar Galactica RPG campaign.)
First off, I had to get a general idea of how fast BSG ships move — using the speculations over on Battlestarwiki.org, I worked out that the sublight Speed Rating in BSG is rough half the percentage of C; in other words, Colonial One with its Speed 6 is capable of up to .12C. (Yes, that means raiders are capable of .18C — really bloody fast…but it’s sci-fi. Roll with it.)
Now that we know how fast the ships can go, we need to know the distances involved in traveling around the Colonies. The map specifies an SU as the distance from Caprica/Gemenon’s barycenter to the sun — about the same as an astronomical unit (handy!) or eight light minutes. We now have distance pegged from light speed. We can get fancy and measure the orbits on the map, but I’m not quite that OCD — each of the four systems seem to have their outer planets orbiting at roughly 5-6SU. In each of the four systems, that means that the Colony worlds are never more than roughly 2.5SU away from each other. You can assume that a trip from, say, Picon to Tauron at their furtherest from each other, take a liner like Colonial One would take about 2.2 hours, but a trip out to Persephone would be about 6SU, which would take a ship like Galactica about five hours at flank speed.
For communications time, figure the rough distance between the worlds in SU, times by eight, and double it for a return message. So if Picon and Caprica are at periapsis (closest distance) the time to cross .2SU is 1.6 minutes. If Caprica and Tauron are 1.5SU apart, receiving the latest Caprica Tonight broadcast would have a lag of 12 minutes.
What about between the stars? Helios Α and Β, and Helios Γ and Δ are both locked in barycentric orbits with each other, with a distance of 60 and 70SU respectively, and both pairs of stars are locked together at about .16LY. A message sent between Colonies in Helios A and B would take between 7.3 hours (for periapsis) and 9.3 hours (at apoapsis.) This means Galactica at full burn would take between 73 and 93 hours to cross the distance from Tauron to Virgon, depending on their position. You would have comparable times between Helios Γ and Δ.
For example: Using this map and speed rating, the old girl was, in the miniseries, hell and gone from anywhere when the attack began. It was roughly 30 minutes to get a message to Caprica, so she was 3.75SU away…out near the Erebos asteroid belt. We could assume she was on her way home from Scorpia Yards, but since they specified the ship hadn’t done an FTL jump in decades, she did it sublight. The distance between the two pairs of stars is .16LY. Even at full speed, Galactica would take almost two years to transit from Scorpia to Caprica.
That means that travel between the four stars is perfectly doable at sublight speeds and would explain why there were a wealth of non-FTL ships plying Colonial space. One thing it does suggest is that to cut down on communications latency, the Colonies use some kind of courier service(s) to move data between the two pairs of stars. I envision a kind of packet boat that jumps from, say, Caprica to Libran, does a data dump of bank records, government documents, express mail, etc. and that from a central hub the data is broadcast out to the destination worlds. Government, military, and financial data is probably shipped daily, but personal stuff might go weekly.