Hi @bencash,
Yes, unfortunately the conda environment solver seems to be really (and increasingly?) slow.
I just tried it myself and quit after waiting 30 mins.
You should use the new fast solver mamba:
$ conda create -n cylc8
$ conda activate cylc8
$ conda install -c conda-forge mamba
$ time mamba install -c conda-forge cylc-flow cylc-uiserver
...
real 0m50.282s
user 0m17.975s
sys 0m2.604s
$ cylc version
8.1.0
That took 50 seconds including solve, download, and install 
I’ll suggest to the team that we update our installation instructions to include this advice.