Ok - my best guess is that your jsn_gruve_pro template is using bootstrap glyphicons which do not include icon-clock.
This is a fairly common issue with bootstrap templates and joomla because joomla doesn't implement the bootstrap icons as standard. And when a template like jsn_gruve_pro or a framework like T3 implement a bootstrap template they replace the joomla definitions (a specific font used by joomla) with the bootstrap ones (a different approach) and do not provide a compatibility mapping for the joomla icon classes.
Where the template uses fontawesome (which has a superset of bootstrap fonts), it is possible to map the joomla icon-classes onto similar icons. I have fixed this for T3 (see
http://t3-framework.org/discussions/icon-compatibility.html) and this same fix can be used by any framework which is using fontawesome.
However, whilst you can use the same technique to map joomla icon classes to bootstrap glyphicons, the number of icons in bootstrap is much smaller than fontawesome, and there isn't a clock symbol to map onto.
And the bootstrap approach for icon mappings cannot (as far as I know) co-exist with the joomla approach so you cannot use the joomla icons alongside the bootstrap ones.
I guess if you paid for this template, you should go back to joomlashine and ask them to provide compatibility for joomla icon classes - which they can do by implementing fontawesome and following the same instructions as for T3.
Sorry I can't actually suggest a quick fix.
S