On a wait means that the place is so full, every table is full and lets check this out, shall we?
Lets say that each table has a 45 minute turn around. That averages out to 10.5 table per 8 hour shift. Using your numbers of three per server, you have 32 tables per shift. Lets low ball this, shall we?
Assume each table turnover is one person per table and has a standard dinner fair with 1 glass of wine which comes to about 18 dollars...That is 3 dollars 60 cents per tip. Multiply that by 32 tables and you have 115 dollars and 20 cents. Divide that by 8 hours and you have 14 dollars and 40 cents per hour.
Remember, this is low-balling it. the Olive garden will probably average about 3 people per table, so you can take that 115 dollars and multiply it by 3 to get 345 dollars a night. Just in tips...Oh, but lets add that 2.13 per hour for 8 hours and we get and additional 17.04 for a grand total of 362.04 for that night were we had a 5 hour wait.
Now, lets see those same 8 hours in action at minimum wage. 7.5 per hour for 8 hours comes to a healthy 60 dollars day! Wow! Go minimum wage!
Pretty simple napkin math, and should not be beyond even you.
Your not lowballing at all. You took a few assumptions.
1) everyone drinks, completely false. At Olive Garden, a decent resteraunt, the average person spends $12, not $18. Kids are cheaper, they bring the average down.
2) you are still assuming they are on a wait for 8 hours. They aren't. 5 nights a week they never get on a wait. The 2 nights they do, it lasts for less then an hour. Your math doesn't matter, in a 5 hour shift they pick up 10 tables. This is real life. Their average sales in a night are almost always <$500.
3) You are assuming that everyone tips 20%.. Not even close. If a server gets 15% total they are doing really really well. 20% is max in almost every circumstance. Everyone gets stiffed from time to time. Even the best ever. There are just cheapskates out there.
So lets assume $500 in sales at 15%. That is $75 in tips. Now they have to share 3% of sales which comes out to 15. 75-15=60.
So if they are a really good server, and its a good night, in 5 hours they make $60.
Slow days? I've seen people work for 2 hours and not even get a table. Then get sent home.