I was able to install atom using the same command, so the package is OK
That mirror is also OK. I tested by clicking on https://mirrors.rit.edu/solus/packages/shannon/a/atom/atom-1.56.0-140-1-x86_64.eopkg and it displayed a file download dialog.
The problem is likely the network between you and that mirror. As others have said, just keep trying and eventually you'll be able to install the package.
You can check the network between you and that mirror with this:
ping mirrors.rit.edu
You'll see output like this. Pay attention to the "time" bits. This should be 200ms or less, ideally. (Press Ctrl-C to stop the output). If you see really large numbers there, that's network slowness, which can cause timeouts like you were seeing.
❰tracey❙~❱✔≻ ping mirrors.rit.edu
PING smoke.rc.rit.edu (129.21.171.72): 56 data bytes
64 bytes from 129.21.171.72: icmp_seq=0 ttl=38 time=56.033 ms
64 bytes from 129.21.171.72: icmp_seq=1 ttl=38 time=55.790 ms
64 bytes from 129.21.171.72: icmp_seq=2 ttl=38 time=52.264 ms
64 bytes from 129.21.171.72: icmp_seq=3 ttl=38 time=55.360 ms
64 bytes from 129.21.171.72: icmp_seq=4 ttl=38 time=53.155 ms
^C--- smoke.rc.rit.edu ping statistics ---
5 packets transmitted, 5 packets received, 0% packet loss
round-trip min/avg/max/stddev = 52.264/54.520/56.033/1.521 ms
Good luck 🙂