MK-677 was officially tested with 25mg/ed for two years.
YK-11 was officially not tested in humans nor in animals
D). Because of the unknown effects, pathways and toxicity I wouldn't run YK-11 more than four weeks.
MK-677: 25mg/ed, before bed in the evening is optimal.
YK-11: start with a dosage as low as possible. Because of the unknown half life, take it at least three times per day (every 8h). I personally wouldn't use more than 5mg/ed, but that's up to you.
YK-11 is going to be really interesting when using more than 12 weeks. Why? Because it's effects on the follistatine level. In such a short period of four weeks (six, if you are brave) you won't build up that much muscle mass, it's a process which takes its time.
A user used RAD-140 together with YK-11 for four weeks and the effect was not that bad, how the wrote that.
MK-677 is well studied (if you can say so), in comparison to YK-11. Before yates84 says I'm overdramatizing again (lol): it's fact that its (neuro-)toxicity is not known. It's also not known if it has a mutagenic/teratogenic/carcinogenic effect. So: happy research
Always have a SERM and an AI on hands. YK-11 is in my opinion not a SARM, it's an AAS. Bloodtest would be the best way for monitoring your health.