Compare commute times between routes.
Comparing routes is only useful once the per-trip difference is scaled to how often you drive it. Seven minutes a leg sounds trivial and is nearly six hours a quarter at two trips a day, five days a week — which is the figure that justifies a longer but freer-flowing route. The difference is signed, so a negative result means Route B is the slower one, and the verdict states plainly which route wins rather than leaving you to read the sign.
Difference
Per trip = Route A minutes - Route B minutes; positive means B is faster
Scaled saving
Hours per week = per trip x trips per day x days per week / 60
Not necessarily. Reliability often matters more than the average — a route that is three minutes slower but varies by two minutes beats one that is faster on average and varies by twenty, because you plan around the worst case.
It can, but not always. Steady flow at moderate speed is more efficient than stop-start traffic, so a route that is longer in distance and shorter in time is sometimes cheaper in fuel as well.