I would say that 1 hour 40 mins is enough time to connect from T3 to T1 at MAN.

Most of the BD longhaul flights arrive about 20-30 mins earlier than scheduled anyway. As your in C you should get off first and therefore beat the queue to passport control. MAN baggage delivery is hit and miss. Although ive never had to wait more than 30 mins for baggage off a BD longhaul flight. The distance from T3 to T1 isnt that bad. You could walk it at a moderate pace in about 10-15 mins max.

All things considered i would go for the 08:45 departure.