90-100 minutes to see all 4 characters has been my experience over 2 visits! 
Plus, Crystal Palace canāt seem to seat on time, 15-20 minutes late! But if I had a kid who wanted to visit with those characters, I would go! Beats standing in line! I wonāt be going back either with my family, unless somebody wants me to go with them.
At other character meals Iāve been to (H&V, Topolino, and Garden Grill, we see all 4 character 2-3 times in 90 minutes.
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The quickest and easiest way to determine a budget is to use the cost of the Dining Plan for the two adults and 2 kids (baby is free). If you want 2 snacks per day add the cost of another snack per day. I think the average cost for a snack is $6.50. Somebody else will have a better estimate because I donāt calculate my dining costs ahead of time.
We have never bought the Dining Plan because we always come out ahead paying cash. BUT if you are doing a character meal each day, it may be worth the Dining Plan, especially if you do lunch and dinner buffets, which are more expensive than breakfast character buffets.
If you want to do a better ballpark, you can peruse the menus for the restaurants you may want to eat at, like others have said.
If you are paying in cash, it is worthwhile to have the latest breakfast ADR at buffets that also do lunch. You get breakfast and lunch options for the breakfast price!
When Iāve done H&V, I do a late lunch, around 1:45 pm. I donāt gorge but I donāt need to eat the rest of the day. Well, maybe a snack waiting for Fantasmic!
If you do the Dining Plan, pick lunch or dinner for the TS meal, since lunch and dinner are more expensive than breakfast.
I do feel like Crystal Palace is one of the ones that it takes longer to see all the characters. Hollywood and Vine also. But if you are missing a character meet, about 3/4s into the meal, ask the server if that one is coming by. They can sometimes advocate to make you one of the first stops when that character is back in the area since they want you to leave soon.
Iāve never missed a character nor sat at a character TS more than 1.25 hours total.
I just went into the app and did a mock order for my family at Cosmic Rays. It was $48 for 2 adults and 2 kids with 2 extra bottles of water.
I also budget out every table service meal separately - which is easy because we have 3 scheduled prix fixe meals (2 character, 1 at space 220). I make sure to add one cocktail for DH and I, plus tax and tip. Space 220 and Chef Mickey dinners will run me more than $300 each for 2 adults and 2 kids (both kids under 10). 
This is a for certain
We had 10:30
Checked in as soon as DME said we could - maybe 10:20
Seated at 11:05
I had read a tip to check in in-person about 30 mins prior. We did this (lunch resi). We were seated about 10 mins after our reservation. If we had been just a few mins early we may have had to wait a lot later. Who really knows. But I think it bothers me more for them to be late than for me to be early and have planned down time while we wait.
I also checked in personally at 10:40 āto make sure we were checked inā 
I was told they were running behind
@stlouie the characters here are my sisterās favs but sheās good with Cape May or Tusker House for awhile.
Probably because the characters take so long. People hang around the tables longer than anticipated.
I do recall you saying that. I adore Pooh and friends but it takes WAY too long for them all to come around once!
I was there 3x in 10 months. In 90 minutes, all the characters came around 3x. I find 90 minutes an acceptable amount of time to graze the buffet a few times, interact with the characters, and chillax while watching others interact with the characters.
Both times I was at CP, the characters came around just ONCE in the 90-100 minutes. We were done eating and just waiting. CP is a huge restaurant compared to other character buffet restaurants. Thatās probably why it takes so long!