Depends on if you have any dissociative tolerance.
If not, I'd say 40mg will get you to borderline m-hole. However, I've always found the m-hole and even the "area around it" so to speak, to be very set and setting dependent. You could take 30 or 40mg of good MXE and hole with meditation, yet take 100mg with friends and not reach it.
As for duration, I usually account for 45-60 minutes to peak, 3-4 hours of peaking, and then 1-4 of coming down. The comedown mostly depending on smoking weed.