I allow up to 5% of my investible assets to be involved in my short term "schemes and crazy ideas." But I'm not sure I'd call it "day trading" which generally involves holding some asset for less than a day. I've been doing it as a hobby for many years.
The bulk of my equity investments are in broad based index funds like VTSMX or SPY. But I get in and out of some micro-caps from time to time and do OK. And I have a few stocks I'll wind up holding for some months. Also, a close family member works for start-ups and other small companies and changes jobs frequently. I like to get ideas from her and have made some money with stocks based on her specific industry knowledge.
I like learning new things as a geezer and getting into some short term trading, covered calls, preferred stocks (really interesting!) and bonds is very entertaining. Lots of information here on the board to be harvested and I tip my hat to the folks I've been learning from. And having a bit of "skin in the game" keeps my geezer mind into it.
It would not change our lifestyle if I completely lost the 5%. But, so far, I've done a bit better than my index funds and enjoyed the activity. The biggest downside is getting everything set up so when I'm away from my home desk for weeks at a time, nothing/little needs attention I'm not comfortable handling from my phone or tablet in short order.
Much of the practicality of doing this as a hobby is your personality. I've never, not once, not ever, never, been tempted to violate my 5% rule. Right now, I'm well below 5%. In fact, I'm usually well below 5%. I've never bet at a race track, purchased a lottery ticket, been to a casino or done online betting. None. But I do like to learn about investing and having some modest skin in the game keeps me interested.