Pinching out a layered clematis?

Last year I planted 2 Montana type Clematis, one on either side of a wooden arch. Both grew well in the spring until I witnessed a squirrel uprooting one side. The other plant flowered around May and now has several new shoots, so I have layered two shoots into pots. The shoot tips  are growing quickly and becoming  too long for the pots and canes - is it safe to pinch the tips out to shorten the potential new plants before I am certain that rooting has taken place? It’s only been about 5 weeks so far. Thank you for any advice.