How do I tell the `date` command to only show the time?

date +%R

will show you the 24 hour time, and

date +%r

will show you the time in 12 hour format. date +%H:%I also works.

Check out the "Conversion Specifications" in the manpage for more variables to pick and choose.

Current time 24h format:

date +%R

Current time 12h format with AM/PM:

date +%I:%M%p

date +%H:%M 

for 13:45

date +%H:%M 

for 1:45

"uptime" 

will tell how long the system has been running (along with other information) check man entry for uptime