Try carefully chipping or scraping off the excess with hard plastic or wood. If that's stone, a white vinegar solution may remove the balance of the unwanted grout.

Were the joints supposed to be so wide and irregular?

Wait 48 hours to clean grout????? More like 20 minutes. He should have waited around.

Post this over in the bathrooms forum. That's where the tile pros hang out, and might have some other solutions to remedy this after the fact.

I just want to say how sorry I am that this happened. Clearly this person had no idea what they were doing and I hate to hear that you had to save up and paid him in cash. Hopefully someone can help you limit the damage.

Is this a glass mosaic tile or a stone?

Is the grout a normal mix, or epoxy-based?

If it's a normal mix and glass tiles, you can consider using a weak solution of muriatic acid to help dissolve some of the grout. If it's epoxy based, you will have to use a heat gun to soften it - and you're better off just tearing it off and starting over (really hard to get epoxy grout off).

Here's what I would do - tear it out & start over. The joints will take so much work to make them look "okay" at this point, you'd probably spend less time in the end if you started over. I say this after the tile guy our GC hired required 3 rounds of re-work to touch up joints in our tub/shower ... and then I still spent a day getting them really right.

Muriatic acid is a reduced strength hydrocholoric acid and should only be used as an absolute last resort, preferably only by someone with prior experience with it. Just the act of diluting it can cause severe personal injuries.