We are talking about battle station with a hyperdrive. And there we have to wait till it orbits around Yavin to get a shot at the moon.
We know why they didn't blast the gas giant with the superlaser out of the way.
But why didn't they navigate DS1 so that it had a clear shot at the rebel moon in the first place?
And why couldn't it orbit faster?
(Source: Irregular Webcomic Strip #507)
They didn't make a microjump because Hyperdrive doesn't work in a gravity well. They probably didn't jump directly to a spot where they could target the moon immediately because they didn't know the precise location of the moon within Yavin's orbit, and they happened to come out of hyperspace on the wrong side of the planet. Besides, they were (at least Tarkin was) very overconfident, so what if it takes them a little bit to get around the planet?
I believe that Han Solo said it best:
Traveling through hyperspace ain't like dusting crops, boy! Without precise calculations we could fly right through a star or bounce too close to a supernova, and that'd end your trip real quick, wouldn't it?
From this we can infer a number of things:
If Han, as one of the better pilots in the galaxy and with a specially modified ship, exhibits this kind of caution, then of course Imperial pilots of a larger ship are going to be even more cautious.
Common sense would therefore seem to dictate that you come out some distance from your objective and make a normal flight from there.
With the computing power they have it seems unlikely that they wouldn't know the position of the planet when they arrived. However, it would be silly to go out of their way in hyperspace just so that they could come in to the system with the moon already in range.
Their arrival in the system would have been based on a most-direct hyperspace jump, which would be standard practice for hyperspace navigation under all but the most unusual circumstances.
Considering the balance of forces, the destruction of the Death Star would have been inconceivable and certainly wouldn't have sweated the 30 minutes it took to orbit the planet.
As per the comic, you can't orbit faster without increasing the orbital altitude. You can't just stay at the same altitude and "go faster". Orbital motion doesn't work like that. Also, moving large ships is very often a slow and imprecise task.
To give a nautical example, it's not unusual for a fully loaded modern supertanker to take 3~8 km to complete a braking maneuver from its normal cruising speed. This means if you're cruising along and decide you need to stop, and you throw your engines in full reverse, it's going to take 14 minutes or more to stop.
And while some large ships have maneuvering thrusters or bow/stern thrusters that help it turn without moving forward, they're mainly used for docking. For normal turns out at sea, a large tanker usually has a turn radius of over 3km.
A space station like the Death Star is going to have a lot more momentum and even less agility. Plus, it's much harder (takes more energy and time) to brake in space. So simply waiting for the orbit of the Death Star to put itself in position for the shot does make sense.
Even in space, there are gains and tradeoffs when it comes to size.
Pseudo-scientific explanation:
The strong, complex tidal forces near Yavin IV present a significant hyperspatial navigational hazard to a vessel as large as the Death Star. To mitigate this, the Death Star dropped out of hyperspace at a point where Yavin, Yavin IV and Yavin's sun were all roughly in alignment, and then orbited the planet to reach Yavin IV. This is a standard manoeuvre for ultra-large vessels.
The real reason:
George Lucas thought it would be more exciting that way.
