While the roads on the Chinese side of the border are entirely paved (with perhaps some exceptions on the pass near Paiku lake and the stretch of 60 kilometres under construction roads near Saga), the “roads” in Nepal are in terrible condition and under construction. Expect sand, gravel, rocks, traffic (mainly trucks), large flat slippery stones hidden under sand, pot holes, possibly deep mud (after rain) and intense heat and dust. Furthermore, there are at least half a dozen time consuming military checks in between Rasuwa Ghadhi and Kathmandu.
Although its only 142 kilometres from Rasuwa Ghadhi to Kathmandu, you will need at least 8 hours, possibly more. We therefore recommend to stay in Dhunche (GPS: 85.29810999999995, 28.1079892 / altitude: 2,148m) overnight, which is 28 kilometres from Rasuwa Ghadhi. Note that some GPS systems have trouble navigating you on the Nepali roads since the newly carved tracks are not yet mapped. Locals we talked to estimate that the road construction will take another 4 years to be completed. You can estimate that you will enter Nepal and be done with immigration and customs after 2PM Nepali time.