Well if folks can't resist temptation and purchase plants, and those plants get killed by frost, then buyers must spend more money in buying plants again -- so increased sales for the seller.

I'm north of you and in my area it is generally unwise to plant things outside before Memorial Day. If you see plants you like and are able to/don't mind bringing them back in if freezing threatens, then go for it. I actually did by a package of cannas today that I plan on potting up tomorrow. If it is going to be too cold outside, I can bring them in. But this way I can get them started growing now (otherwise they seem to take forever to get going for me).

You can plant frost tolerant crops and always throw a sheet over them if a hard freeze should happen. Here in MN they are already filling up with all the summer annuals. Not only is the threat of frost a possibility, these plants also like much warmer days and nights than are average right now. I saw people buying tomatoes the other day.

I have potted up some containers with pansies, violas, kale, pussy willow stems and some frost tolerant grasses. These should serve me fine until the end of May/Early June when the rush is over and all the annuals go on sale.

I think its a bit too early to trust Old Man winter not throwing a huff and giving some frost in the next couple of weeks anyway.
We use the 24th of May---the Queen's Birthday--Victoria that is, as our guide to when we set out our annuals.
The holiday is though put at the nearest Monday to the 24th, therefore can be anywehere from the 18th to 24th.
Frost is not unheard of even at the later date and we watch out for what we might have to do to protect our investments.
We are fortunate in living near a large body of water--- and therefore, frost is not so harsh and can be avoided by most simple ways. Bodies of water can modify frosts that are more dangerous to inland areas.

Still, in northern Indiana, south of Chicago, I would think two weeks yet should be more the time to consider in your area.

Using the Memorial Day weekend is stretching it a bit, I think--heck if we can plant on the weekend of the 16th--(holiday is the 18th) I think you can get away with a few days before that....at least.