I normally complete ignore this "I was one week in the warp but x weeks away in reality" just for simplicites sake.
To us, it's one of the more flavourful aspects of interstellar travel in the Imperium. In that week you spent in the Warp, several months may have passed in Realspace, and that suspected Slaaneshi cult you were sent to investigate may have risen up to take control of the Agri-World you're just now arriving at.
And of course, weirder things can happen. Like, you might arrive at your destination at a Realspace point in time that pre-dates your departure.
Obviously tastes (and focus) differ, but I think the timey wimey aspect of Warp travel is pretty awesome.
I'll just say that they have a few options, either the long trip outside the warp, warp travel to Dreah and smaller craft to Solomon, or Warp travel to Solomon. They'll obviously have the drawback of having less opportunity for their own investigations or earning cash on their own.
Interstellar (between stars) travel in the Imperium of Man is Warp travel or nothing. The travel times I listed earlier were for Warp travel: 24 hours spent in the Warp means some 50 days have passed in Realspace.
Interplanetary (between planets in the same star system) travel in the Imperium of Man uses technology not too different from what's available to us real-world Earthlings right now. The notable difference is that the IoM has gravity technology, which lets them accelerate at speeds that would injure or kill the occupants of a space ship without grav plating.
But even so, interplanetary travel in 40K isn't drastically faster than it is for us real-world human beings of today. We're still talking weeks, even months, of travel.
In retrospect, they're acolytes and need to learn their place. Their inquisitor may have just decided they're taking the long route to reflect on their own actions read here as (prepare themselves for what's coming next because he's putting them in essentially a suicide mission that is The House of Dust and Ash.)
It's completely in line with the fluff to tell your Acolytes that it will take them 3-4 weeks of Realspace travel time to get from the outskirts of the Solomon system, to Solomon itself.
The journey through the Warp to get to the system may only have taken 20 hours from the perspective of the Acolytes (while 60 days passed in Realspace), but the Warp jump doesn't actually take them to the planet, it just takes them to the system where the planet is located.
According to the fluff, it works this way for safety reasons. Essentially, jumping around inside a star system is dangerous because it'd difficult to determine if there's something at your entry point to Realspace. So to avoid plowing your big, fancy ship into a planet, you enter Realspace at the edge of the star system.