I mean, people exchange their time for money when they work, so this is basically the same but more hardcore as she probably loses a fair amount of time every time she uses the hourglass. So I'd say, "Just use it in moderation."
@WhiskeyWolf he didn't go to the party to surprise her, he went there to make sure that Mielle is not the one he met. he already knew, but he wanted to make sure.
In the novel she started with 100 gold coins worth of chips
She only bet when noone else won
At first she gained 100*10
The next day she gained 1000*10
And since she can only bet 1000 coins max she did it for few extra days
She probably won 50 000 coins in total