Hyper Drives Part 1
Imagine if we took a drill and (somehow) bored a tunnel from the North to South Pole. The tunnel is kept in a vacuum, the walls frictionless. We take a sealed car and drop it on the hole. After 38-42 minutes the car arrives at the South Pole. Gravity draws the car to the center of the Earth and afterwards slows it down.
We soon realize there are few people who want to go from the North to South Pole and dig a new tunnel from Antarctica to Australia allowing researchers and easy commute. We drop a car into the tunnel and discover it also takes about 40 minutes to drive. In fact any tunnel connecting any two points on the Earth's surface will allow a gravity assisted transit in about 40 minutes. The transit time is a function of the density of the planet and the gravitational constant.
Assume our universe is a skin over 'hyper-space'. Stars and planets are laid out on the skin. If you break this skin then hyper-space does its best to drag you in. It could be a very elaborate means to self destruction but star faring races manage to create tunnels to objects several parsecs from their point of origin. The hyper-force acts like gravity on our transcontinental tunnel cars, pulling them to their destination. The time is dependent on the 'density' of hyperspace and some other constants. It works out to about a week, regardless of the distance covered.
A few cautions to the wise. Hyper-space is like the Earth's mantle and core. It has areas of greater or lesser densities. The trip time will vary a little, if you're timing a fleet action and expect every vessel to magically appear at once you might be disappointed. This discrepancy can be reduced by using ships of the same class or at least similar size and drive capacity.
Stars and planets, really all material objects, create ripples in hyper-space. These can cause ships to come out of hyper-space in a longer or shorter period of time, or miss their destination entirely.
Currents in hyper-space also can push a ship- off course. These currents are detected by their effects on the ftl drive. Different currents cause different components to overheat or draw more power. A savvy pilot and navigator team keep records of currents on different courses, knowing when they are likely to turn up and compensate for them. Currents have less extreme effects but they can cause wear on your drive and result in being a few million miles off course or even a few AUs.
Currents also change over days and weeks. A navigator's course is calculated take them into account, based on reports of ships that made the trip recently when they can. Such a course has a shelf life of a few days or hours. Then the currents shift. Some systems for unknown (or classified) reasons have a regular storm of currents around them and are red listed. Ships are warned not to approach. They are often carefully studied -from adjacent systems.