I'm sorry your introduction to the board is under such sad circumstances, HunNica.
Unfortunately, all dogs and all cancers progress differently so it's hard to make predictions. However, with our Priscilla, the nose bleeds became gradually more frequent and more severe. We knew we were nearing the end the day she died--we'd made an appointment that evening to have her put to sleep. Priscilla just took matter into her own paws...
Priscilla's cancer never spread out of the nasal passages, though, as is the case in your dog, so I'm not sure if you'll see the same pattern or not.
Follow your heart and take it day by day. When waiting will give you
time, but bring your girl
no joy, you'll know it's time. It's a hard decision to make, but whatever you decide and whenever you decide it, if you make your decision out of love, your Vizsla will never fault you for it.
Good luck, HunNica. Most of the members here can relate to what you're going through--the board is very supportive. Please keep us posted on how things go. We're here if you need to talk or rant or just need a hug.