Buds as in flower buds?? This is surprisingly early for a type 3 clem to be showing flower buds............Perle is typically listed as a midsummer (July) into fall bloomer.

If it is showing buds now, I would just skip the pruning. Pruning is not a requirement but more of a means to tidy up deciduous clematis after winter and keep their size in check. If you really want to, you could prune now and hope for a later, more expected timing bloom cycle but just not sure how it will respond this late. Won't hurt the plant at all - just alter the bloom sequence.

Thanks gardengal - it's only showing leaf buds, not flower buds so I'll take a deep breath and cut it back - but not too hard. Hopefully all it will do is delay the flowering as you suggest.

If the buds are not flower buds, then you should be fine. Type 3 clems bloom on new growth and there is still plenty of time for new growth to develop and set flower buds before the expected flowering time.