cc @infinisil

What's the error when starting without this delay?

There is no error. Even systemctl --user status shows everything is fine but imwheel does nothing. For instance if you would use imwheel to set high speed of scrolling wheel, after the boot / start of session this would not take any effect. Service is running but has no effect at all. After restarting the service, imwheel would start working. I don't really know how imwheel works but it seems it's racing with something and if it starts too early it simply doesn't work.

No logs in journalctl --user -u imwheel -e?

@infinisil no, only successes. This is the log from several reboots.

-- Reboot --
Aug 22 13:59:11 nixos-mainframe systemd[1976]: Started imwheel service.
Aug 22 13:59:11 nixos-mainframe imwheel[2051]: INFO: imwheel is not running as a daemon.
Aug 22 13:59:11 nixos-mainframe imwheel[2051]: INFO: imwheel started (pid=2051)
Aug 22 13:59:11 nixos-mainframe systemd[1976]: imwheel.service: Succeeded.
-- Reboot --
Aug 22 14:23:36 nixos-mainframe systemd[1984]: Started imwheel service.
Aug 22 14:23:36 nixos-mainframe imwheel[2061]: INFO: imwheel is not running as a daemon.
Aug 22 14:23:36 nixos-mainframe imwheel[2061]: INFO: imwheel started (pid=2061)
Aug 22 14:23:37 nixos-mainframe systemd[1984]: imwheel.service: Succeeded.
-- Reboot --
Aug 22 14:40:32 nixos-mainframe systemd[1977]: Started imwheel service.
Aug 22 14:40:32 nixos-mainframe imwheel[2045]: INFO: imwheel is not running as a daemon.
Aug 22 14:40:32 nixos-mainframe imwheel[2045]: INFO: imwheel started (pid=2045)
Aug 22 14:40:32 nixos-mainframe systemd[1977]: imwheel.service: Succeeded.

Hm well I guess if we can't figure out the actual cause, this is the next best thing.

Oof and I'm also just noticing that this package hasn't seen an update in 16 years! Is there nothing more maintained out there?

I'm not much happy about this either. It always feels deeply wrong to fix synchronization issues with sleep. The only reason why I was brave enough to open this PR was that I've seen redshift service uses this as well.

Yes the package is old as hell. I'm not a maintainer of the package itself. That's being said I also used it several years ago on Arch (https://wiki.archlinux.org/index.php/IMWheel). I'm not really sure about alternatives but we can definitely look into it. Anyway in case we would find something neater I would still be in favor of merging this fix for folks out there and then adding some deprecation notice with recommendation of switching to alternative.