I've been using rondo (and resin) and if you have temperatures around or under 0C... so it's freezing cold winter - I advise against trying and just waiting.
It'll take literally days for it to harden, very long time and overall it's just better to wait til it's warmer again instead of fighting with it. However, it is most certainly possible - I've hardened most of my armor during winter and such very cold temperatures. Not worth it however.