There is no 'deadline', my dd#2 was still night-feeding until 13 months, it's very individual I'm afraid!
Could you post ds's Eat schedule again, I'm afraid I found the first one a bit confusing (sorry!) - is it something like this?
5am 50ml milk
11am 100ml milk + some solid foods
2pm 100ml milk + some solid foods
6-8pm 100ml milk
midnight 100ml milk
3am 100ml milk
At 8.5 months, solid foods are still more about learning than about eating, babymilk (breast or formula) is the thing that provides babies' nutrition. Until 12 months babies should be getting a minimum of a pint (approx 575ml) of babymilk in 24 hours, but the best way to work out how much ds should be taking is to remember back to how much he had before you introduced solid foods - this is how much he should still be taking now, with solid foods 'topping him up'!
With this in mind, I would suggest that you reorganise your Eat schedule to get him taking a bit more milk more regularly during the day. The schedule below is a suggestion (I've based it on 1 nap in the day as that is all you mentioned in your first post), but obviously as you are working, you might have to modify it to fit in with your family's other commitments:
7am 150ml milk
8am breakfast solids
10.30am 150ml milk
Nap
12.30pm lunch solids
3pm 150ml milk
4.30pm tea solids
7pm 200ml milk
Bed
The solid 'meals' don't have to be big quantities, just as much as he wants to eat, and could even be offered as finger food if you like? He might still want a late evening milk feed say 10.30pm, but with so much more milk in the day-time I would think he wouldn't need any more at night.
Hope this makes sense, please correct me if I've made any wrong assumptions!
Ax