The timer in the resources tab is a .exe file, which is for windows.

And yes, i did try to use wine to use it (wine opens .exe files on mac, sometimes) but it didnt work.

if anyone knows of a different timer, that would be awesome.

Sadly this is the only in-game timer for minecraft. I as a mac user have just recorded my good runs and timed out the loads by cutting out everything but the gameplay in iMovie. I hope this is helpful. EDIT - Alternatively, there is a statistic that shows minutes/hours played. There is also one that shows tick count and if you take the number of ticks and divide by 20 that is your In-Game time in seconds, just then convert to minutes.