When using editor extensions and switching to the test area which has no time I get a crash with this error:

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/EE_TESTSURFACE_player"
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 have the same problem, crashes blueprint sandbox, Probably at a guess it doesn't know what planet it is on or what the day night cycle is when in sandbox mode.

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.

Sweet, I actually prefer the frame as well!