Pruning group 2 clematis can be pruned lightly in both late winter
or early spring as the new growth buds swell and again lightly
after the first bloom flush to encourage later blooming.

Seem like the key word is "lightly"; otherwise, the plant will delay
flowering as you mentioned.

Hard pruning in late winter will reduce the size of the plant and
delay blossoming until early to midsummer, but you will get a
heavier set of flowers. Clematis will grow towards sunlight, so
your reduction in size may not be very long lasting. I prefer to
grow Group 2 clematis through a shrub or small tree, so that
their 'naked' lower levels are not as noticeable.

Oh well... Seem like I have chosen the wrong type of clematis for the
trellis. But this probably is OK because I have already planted some
3-ft tall plants in front of the trellis to somewhat cover the empty
space in the trellis.

I think I will not bother to prune it. I probably should spend the
time pruning the roses instead of the clematis. OK, I guess I have one
less thing to do around the garden.

Thanks for answering my questions.

Jay Chan