It is too early to worry about your clutch. If they are all alive (no black/green/purple/brown mold and you can see veins) then you are doing just fine.
I've had clutches that never dimpled while others were dimpled almost from the first week (even with nearly 100% in their egg boxes). Dimpling is really a pretty weak indicator of the snake's readiness to hatch. Don't count on it to mean anything.
Your temps are at 88.8 degrees which is just fine. Right now, I wouldn't worry about anything if I were you. Stick it out until they start to pip - you waited this long, I'm sure you can wait a little longer. Remember they actually are supposed to incubate for 60-65 days on average at those temperatures, the thing that is so confusing and frustrating to new people in this hobby is that the trend has been to cut open your eggs earlier and earlier every year.
Wait until day 65 (if they last that long without pipping). I've had them take until day 67 before the first one pipped. There is nothing wrong with your clutch.
Oh, and as far as the post about them pipping and then possibly drowning.... disregard that. I've NEVER seen or heard of ANY snake, lizard or ANY other animal that hatches from an egg EVER drowning in it's own fluids. Chances are that person encountered a baby that was able to pip but died in the egg due to either an internal deformity or a twisted umbilical cord (which happens every now and then). If the umbilicus gets twisted it may cut off the hatchlings yolk supply (they still have a rather large amount of yolk to absorb even after they pip), since it takes a lot of energy to pip and hatch, a twisted umbilicus would essentially starve the baby to death. The only way to tell if this is a possible problem is if all of the other clutch mates have left their eggs and you still have one in it's egg (pipped of course) a day or so later.
For now, don't worry about that, though. IF it does come to that, you can always email me and I can send you detailed instructions to follow that have ALWAYS worked for me to help save the hatchling. Some people say that a twisted umbilical cord is basically a death sentence. I call that laziness. It's simple to untwist the cord, but it does require you to follow some specific instructions and have steady, gentle hands.
Email me if you need any extra help...
sander DOT brandon AT gmail DOT com
You know what to do.
Good luck!