Some Guy:
I think it's safe to say at this stage more is better. Both of the first two paths came for me in the 9th hour of one-day home retreats.
Steph S:
Depends upon the quality of those 90 minutes. In that 90 minutes do you find that towards the end the momentum, clarity, and mindfulness are still really good - or is it a struggle to keep going by that point? If it's a struggle, I'd say you might be forcing it to extend the sit, and so it might not be all that beneficial to increase the time. But if you find the quality of the session is still good at 90 minutes, then yeah sure, increase the time.
Thanks for the advice. I have now increased the meditation time to two hours a day (one sit). As long as I have slept properly and had some coffee, I can easiliy sit for two hours and have actually peek focus at the end of the sit, so 2.5 or 3 hours would be possible if my schedule allowed for it, which it doesn't currently. I can always try to increase the quality of the sit. I'll see what happens...