I was also wondering what was a good time to transplant them outdoors?

You could have/ should have started earlier.
DO NOT WORRY ABOUT FROST when it comes to onions.
My onions (planted in fall) were in the colds down to15F
this past winter. They did not budge.
But, they will not grow much or not at all if it is , say
under 40F.

So, go right ahead and start your seed inside, where the temps will be 55F -65F. and plant them when they are abou 4 - 6 inches.

Better yet , get some sets and plant them. "sets" are grown from onion seeds, by a commercial grower. They just pull them up, cut the top, make bunches and sell them for home gardeners, to give them a head start.

As long as your garden soil is not frozen solid, you can plant seeds and pearl onions any time.

am I wasting my time starting onion seeds now?

Dataspy, probably you are not wasting your time.
In zone 5, probably you can start your onions from seed now right now.
As I said, onions can tolerate freez, snow... But will not grow much
untill night low climb over 35F. So if that is going to be sometime
in mid-late May, then you have still 2 months. O fcourse, if
your seedlings get big enough before that time you can always transplan them sooner.

buying and planting Onion sets is a convenience. Then again, you can do
both ways. A bounch of sets will cost a few bucks.

I start my onions from seed in early spring for zone 6. I find that those I plant from seed do much better than the mini bulbs available from the local stores. I never see the other option offered.

cyrus are you talking about sets or plants?????
FOLKS google dixondale farms. They have plants and a lot of good information if you are not familure with growing onions. YOPPER

yopper, I was talking about seeds. Onions can tolerat freezing
temperatures but seeds will not grow in the cold.
In my zone , you can start the seeds, by direct sowing in the garden
in early fall so thet will grow about 3- 5 inches before it get real cold.
Then they will overwinter and take off in the spring.
Other options are starting seeds inside or buying sets and planting right about the time that lows get to near freezing mark.

In your zone, 3-4, I don't know how you should do it.

Zone 4 here; Well what I do is put out onion starts or sets as soon as The ground unfreezes. That is before the ground can be tilled. Starts are either self sewn early or ordered. yopper all my gardening friends like the dixondale starts. Now sets(stunted onion) the little bulbs in the stores will not grow as big as the starts. They do work well and grow just fine and of course they can be done on the cheap. A bag of 80 is the same cost as a pack of seeds. Well I like to grow onions that don't come in sets(copra candy apple)so mine were started in February. Thank you Cyrus your tips have been great. I just love Alliums!

Curt :-)

Indiana zone 5 here. I heard anywhere from 8-12 weeks. So I started 10 weeks from plant date. My last frost date from the almanac is April 25 South Bend Indiana. I'm closer to Indianapolis which is April 15 last frost date.
My first planting date from Purdue University is April 1 and last planting date is May 1.
So Plant anytime in February and finish by the first of March.

Onions do not have a "Planting Date" per se.
You can transplant your seedlings anytime in late winter/early spring,
when the ground is workable. The only thing is that when it is cold
say, [[freezing rangethere is a frost or even freez, it is not going to harm onions.