Why use NRHO(Near Rectilinear Halo Orbit) is because Orion only has ~1350 m/s of available Δv(change in velocity). Entering and exiting LLO(Low Lunar Orbit) on a direct trajectory(like how Apollo did it) requires at least 700 m/s each way. Entering and exiting NRHO requires ~450 m/s each way so NRHO is within Orion's operational range.
Orion does indeed "hitch a ride" down to LLO altitude but Δv of ~750 m/s needs to be applied to transfer from one orbit to the other. The plan is for the lander to provide the additional Δv for the orbit change. From LLO an additional ~2000 m/s is needed to reach the Lunar surface.
When we consider both Orion and lander propellant(fuel and oxidizer) going to the Moon via NRHO requires at least 33% more. At least is because lander propellant requirements depend on lander design. This is not ideal but since Orion isn't capable of operating in LLO and Congress mandates NASA must build SLS/Orion.
Since you mentioned time I'll briefly touch on the topic. Orion going to or from NRHO and Earth takes ~6 days versus the ~4 days needed if Orion could go to and from LLO. The lander going to or from NRHO and the Moon requires 12+ hours versus the 30 minutes or less for LLO. Minimum layover time on Gateway is ~7 day versus the 2 hours for LLO.