Hi Arjen, I dont know what zone you are in but if your sweet peas have already experienced some frost and your ground is workable, you probably could get away with planting them out, they are incredibly hardy. I usually plant my seeds a little earlier than you did, in August, where they are to flower and let them brave the winter.
They are fantastic.

Call T&M and tell them, they have a guarantee and should replace your seeds. When you get them soak them for a day or so and plant them with your plants, they will catch up.

As for birds, mine dont usually suffer but I dont have any pigeons either. This is all IMHO. Best of Luck. Kat

Arjen,

I start my Sweat Peas every year by soaking my peas overnight in water, then getting a paper towel damp but not too wet as to rot the seeds then put them on the paper towel not touching, fold the towel over and put them in a ziplock bag one large enough so they all lay out flat, close bag. I leave on my kitchen counter and check in a few days when you see roots then take them out and plant. That way you know which ones are good and which ones didn't germinate.
Then from last years experience the deer at my house ate my sweet peas I now have them fenced in. I won't take anymore chances it took them a month to recover from getting munched down to one foot high.
Good Luck,
Kathy

Well I planted the sweet peas a week or two ago an dthey seem to be doing fine! Thanks for the tips!