Travel(ler) Times

Back in the halcyon days of Google Plus – the only social media platform I've ever really liked – I floated the idea of starting up an open-ended, multi-group Traveller sandbox campaign set in a single subsector of space. For those unfamiliar with a subsector, here's an example:

Each hex represents a week's travel time in a starship outfitted with a Jump-1 drive. So, to travel from Regina (hex 0310) to Forboldn (hex 0206) would take two weeks – one to jump into either Ruie (hex 0209) or Hefry (hex 0309) and another to jump into Forboldn itself. Of course, Jump-1 is the least powerful form of jump drive, with others rated as high as Jump-6, the number being how many hexes it can travel in a single week. In my example, a starship equipped with a Jump-2 drive could thus reach Forboldn from Regina in a single week. And so on.
The relative slowness of interstellar travel is an important part of what makes Traveller the game that it is, regardless of whether the setting is GDW's Charted Space or a homebrew one. Since there is no faster means of communicating between star systems, information travels at the speed of the fastest ship available, much as did during the Age of Sail on Earth. This means that interstellar governments either have to delegate authority to local worlds or risk making decisions based on intelligence that may be weeks or even months out of date. This set-up creates a fun dynamic that's very conducive to adventure.
It also presents a bit of a problem for the kind of campaign I proposed on Google Plus. My idea was that I'd have several different groups of player characters operating within the same subsector, each starting on a different world. Their actions would be independent of one another and, unless they were significant in some way, they'd probably never even know about what the others were up to. However, I had hopes that, over time, each group would have sufficient impact on the worlds of the subsector that there'd be reverberations that could be felt elsewhere.
The difficulty was timing. If, for example, one group of characters, acting as mercenaries, helped overthrow the planetary government of Roup (hex 0407), word of that would travel slowly throughout the subsector. Depending on where the other groups of characters were, it might be some time before they heard of it. Furthermore, suppose one of those groups was adventuring on a single planet for weeks of real time, but only a few days of game time. They'd very quickly fall out of sync with the others, creating a timekeeping headache for me as the referee, since, as we all know, YOU CANNOT HAVE A MEANINGFUL CAMPAIGN IF STRICT TIME RECORDS ARE NOT KEPT. 
It's not an insurmountable problem, to be sure. Gary Gygax does provide some genuinely helpful advice on how to manage groups engaged in different activities at different times within the same campaign in the AD&D Dungeon Masters Guide. Nevertheless, it's still a lot to juggle in a way that allows regular play to proceed without interruption. If all the character groups spent no more than a single session on each world, this would be easier to manage, but that's unlikely to be the case. I don't want to enforce an artificial limit like "You must complete your mission on this world in four hours of play or else you must leave" to achieve the kind of campaign I want to run, but that seems to be the simplest way to achieve it and that's disappointing.
Am I missing something obvious? Is there a good way to referee an open-ended sandbox campaign with multiple character groups acting independently of one another without either artificial time limits or having to coordinate several out of sync timelines? If so, I'd love to hear about it.