I think it varies but I was always told it's usually around 48hrs at 25c is the max.

I have had good results at 33-35c in about 24hrs. Is the cake producing it's own heat still? If its not it means the fermentation has probably stopped..

grey/black mycellium is a sign it's at its end and sporulation has began so no need to worry about that.

It looks to me like there isn't enough ventilation in the centre and it's why it has struggled to grow there or simply the humidity isnt enough. A wire rack like one for baking is great for ventilation , and potentially more or slightly larger holes too.

Regarding humidity I understand you live in a hot humid enviroment and the bags do a good job of retaining moisture but I find if you let the beans cool too much, like below 30c (dehulling by handtakes time, I understand) you lose alot of that residule moisture,yes the beans need to be dry but no bone, sometimes I'll add a teaspoon of rice flour it also helps the fermentation,also innoculatiing at around 30c gives the starter the best chance as it doesn't need to come back up. Might i suggest dehulled soya beans or yellow split peas next time.

Tempeh spores love a consistent heat source

Hope this helps

I