Ok done it.

press capacity 1 = x = 30,000 copies per hour

press capacity 2 = y = 35,000 copies per hour

press capacity 3 = z = 20,000 copies per hour

presses x and y start at 22.00

press z starts at 23.30

planned quantity = Q = 350,000

OK

2 presses work for t hours

1 press works (t-1.5) hours

(capacity 1) t + (capacity 2) t + (capacity 3) (t-1.5) = 350,000

xt + yt + z(t-1.5) = Q

xt + yt + zt - z(1.5) = Q

xt + yt + zt = Q + z(1.5)

t = (Q + z(1.5)) / xt + yt + z

In real terms with real numbers then

The two presses work for t hours. The third one for ( t - 1.5 ) hrs

70000 t + 20000 ( t - 1.5 ) = 350000

70000 t + 20000 t - 30000 = 350000

90000 t = 380000

......... t = 380000/ 90000

......... t = 4.2 = 4hrs 13 min

The machines started at 22 hrs, plus 4 hrs 13 min . It ends at 2 hrs 13 min

It ends at 2 hrs 13 min

Ta dah!

Not all my own work, sorry.