Shipping fish is straight forward, but then again its not.
I have shipped a fair amount over the years, most have been successful, some not.
The biggest intangible, that is out of your control is the weather.
You can ship on a 24 hour schedule, but if there is a storm somewhere in between, it could turn out to be 48 hours or even longer. I use 4 day heat packs now, just in case during cool weather.
The first time I shipped, I was assured it would be within 24 hours, but ended to be 4 days before they arrived. Half the fish were dead, luckily I sent twice as many as was asked for.
I also don't like to ship anything larger than 2 inches. When most cichlids get much larger than that, the spines usually puncture even the thickest of bags. When I have shipped larger fish, besides double bagging with the thickest bags I can get, I wrap the entire bag in duct tape.
Even with some smaller cichlids the spines can be sharp and easily do in a bag.
I also always put the shippees phone number on the bag, put a note to call him/her, and try to get the receiver to go to the post office as soon as it opens to pick up the fish if possible. There is nothing worse than having a fish ride around all day, in a hot, or freezing truck.
When I'm receiving fish, I make it a point to be there when the office opens, and get the box before it leaves the facility on the truck. Most flights when I lived in Milwaukee, arrived sometime during the early morning hours (4,5, or 6AM).