I haven't had my coffee yet, but that sounds like you're trying to do things the hard way. Most people simply use various castsequence macros to create rotations of various standard spells.

You claim cooldown bars are too messy, but I'm not sure how having a slew of numbers is any easier to work with. Cooldown bars don't need to be paid attention to in the way that a clock would. It's very easy to see from the corner of your eye that a cooldown bar is shrinking and changing color, as opposed to a simple clock, which is not making any noticeable change other than number increments. And that only becomes more obvious as you start adding a dozen "clocks" for various spells across various toons.

Try Deadly Boss Mods with the Spell Timers mod and/or Group Cooldowns.

Better advice would be learn to use castsequences and toggles so you don't have to keep track of every single spell and cast time and cooldown. That attention is better spent watching enemies, procs, CC and healing. Trying to time things yourself will only lead to a loss in DPS running a mixed team as you get more spells or as things get chaotic. Especially, since as Fenril said, you have to account for lag and latency.