Hi YabadabbingDo
Mate Normally flowering time is 60-70 days for Orange sherbet.
I Always add a week to this.
So you actually probably just on time if you planning to do flushing as most professional growers will recommend.
You are day 40 flower so you have 20 days to add Ripen that's makes 60 days add another feed to it and you will have about 63/64 days gone.
Then do your flush and 12/14 days only PH 6 water. It will take you to about 77 days.
That looks good enough By suppliers recommended Flowering time.
Humidity
It could affect bud size slightly.
Most recommended humidity level in Flowering stage is between 45%-55%.
Article which should tell you what I mean.
With very low humidity, the plant is drawing water from the soil at a very high rate, and if the humidity is too low, the plant is unable to draw water at a rate equal to loss through the stomatal openings. The result is that the plants close their stomata, which slows the photosynthetic process (due to carbon limitations) and leads to stress, slow growth and compromised yield. Under severely low humidity, the plant will wilt and die because even its protective mechanisms cannot offset the water stress imposed by the lack of atmospheric water.
Conversely, if humidity drops much below 50%, crop photosynthetic efficiency may be affected and yield will suffer.
If you have more questions happy to help I'm PM.
Hope this helps.
And good luck with your grow.