The Chatters crowd is worthless for the quick answer (as usual) so here I am.

I have a grid that's 24 columns and 1 row. I want all 24 cells to be a constain size, all the time, whether there is an atom, text, numbers, or anything else within them.

Is there a way to manually set the width or height of a cell?

Previous threads on this topic came to no conclusions that I seen, and were abandoned mid-stride.

Short answer: no, although it's been on my wishlist for future features.

Long answer: maybe with a hacky workaround. I know I played with this a while ago for an inventory system, I'll see if I can dig it up.
In response to DarkCampainger
Found it: (Over a year old! Good thing I don't throw anything away!)

I don't know if it will help you though, as it may not work with some of the elements you'll be using.

If that doesn't work, you could always create 24 grid controls with 1 column/row each :P