Every road category in a map is defined by a speed limit.
When a route is calculated, road category, speed limit, number of turns and road junction are calculated to produce this route.
When you "Minimize Distance" it calculates the shortest possible length of the route, although this can cost you Time because of smaller roads with lower speed limits and more junctions and turns.
When you "Minimize Time" it calculates larger (faster) roads with higher speed limits and takes notice to be the shortest possible (but via larger roads).
If for example, you choose "Minimize Distance" and all the roads are 30 km/h, the length is 30 km, the Time you need is at least an hour.
If you choose "Minimize Time", maybe the length of the route is now 40 km, but via faster roads with 80 km/h speed limits, you need half an hour now.
In the following example in Mapsource Start and Destination are the same.
The purple route is "Shortest Distance" (or "Minimize Distance") and is 30.4 km but it takes 32:25 minutes.
The blue route is "Faster Time" (or "Minimize Time") and it is 1:17 minutes faster but it is also 1.8 km longer.