It looks like this mod doesn't support other surfaces (that might not have a day/night cycle) so I suspect mods like factorissimo will also crash.

I'd also check if other modded planets work properly (hopefully)

The mod What Time Is It (1.0.2) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event WhatTimeIsIt::on_player_changed_surface (ID 55)
Unknown sprite "space-location/proc_4359995"
stack traceback:
[C]: in function 'newindex'
__WhatTimeIsIt/req/whatTimeIsIt.lua:21: in function '_UpdateSurface'
WhatTimeIsIt/req/whatTimeIsIt.lua:75: in function 'UpdateSurface'
WhatTimeIsIt/control.lua:9: in function <WhatTimeIsIt/control.lua:7>

I got a similar issue with blueprint sandboxes
https://mods.factorio.com/mod/blueprint-sandboxes?from=search

The mod What Time Is It (1.0.2) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event WhatTimeIsIt::on_player_changed_surface (ID 55)
Unknown sprite "space-location/bpsb-lab-p-dmikalova"
stack traceback:
[C]: in function 'newindex'
__WhatTimeIsIt/req/whatTimeIsIt.lua:21: in function '_UpdateSurface'
WhatTimeIsIt/req/whatTimeIsIt.lua:75: in function 'UpdateSurface'
WhatTimeIsIt/control.lua:9: in function <WhatTimeIsIt/control.lua:7>

I took it on myself to develop my own version of a clock mod, which supports modded surfaces like Blueprint Sandboxes and also has some other features that I (and apparently other people) missed in this mod: It's About Time! :)

I still hope this mod gets updated at some point, I've decided on a different visual style with my mod and I can imagine some people might prefer the frame-/background-less look of this mod.