Hi 8 weeks is still very young to always get the self settle completely right, lots of things affect their day, wind, over stimulation, over/under tired if you get my drift.
30 mins tend to be OT naps, 40/45 mins UT but it can be a bit hit and miss, personally with my kids things tended to get a bit more predictable after 12 weeks.
They may well need different A times, 5 mins either way can make a big difference at this age.
I wouldn't be leaving them to cry at all really, groaning and moaning maybe but I'd go with shush pat at this age. Do they sleep together?