The lower end of Cisco switches e.g the C3750 Layer 3, do not have a built-in system clock mechanism. As a result, the time needs to be set either manually or by an external ntp time source.
The configuration below shows the commands for setting the time on a Cisco 3750 Layer 3 switch using an external time from a domain controller on the local network.

Log in to the switch using Putty (or any terminal emulation tool).

Display time on switch before clock configuration:
LabL3Switch#sh clock detail
*01:08:07.525 UTC Wed Apr 14 1993
No time source


Set timezone: LabL3Switch(config)#clock timezone CST -6

Set the time to a preferred external ntp time source on local network. In this case, a domain controller(Past post on Active Directory Time):
LabL3Switch(config)#ntp server 10.0.0.20 prefer

Configure daylight savings: LabL3Switch(config)#clock summer-time CDT recurring

Display new and current clock settings: LabL3Switch#sh clock detail
12:32:33.150 CST Fri Feb 27 2015
Time source is NTP
Summer time starts 02:00:00 CST Sun Mar 8 2015
Summer time ends 02:00:00 CST Sun Nov 1 2015