I often work with multiple cameras in my photography.  When I'm photographing events, stage productions and family sessions I typically use two cameras.  That way I can alternate between my favorite lenses, my 24-70mm and my 70-200mm lenses.  The convenience of working with two cameras enables me to switch lenses without stopping to actually exchange lenses on one camera body.  I can catch the spontaneous moments with the right lens.  I've worked with up to four cameras at an event - two Canon 5D's, my iPhone and my Canon Power Shot S120.  

When working with multiple cameras it's critical to synch the date and time.  I use the world clock to set the time for San Francisco, my timezone, down to the second.  Every few months I double check all of my cameras to be sure they are in synch.  That way when I download images in Lightroom, my primary editing tool, no matter what camera I used the photos are in chronological order, which is exactly what I want.  But every now and then my cameras are not in synch.  Whether the clocks are not in synch due to a battery change, new camera or whatever the reason, you can still manage to synch the photos after you upload them to Lightroom by following the steps below:

• This example assumes TWO cameras, but the steps would be the same if you had more than two cameras
• Be sure you are in LIBRARY MODE in LIGHTROOM
• If all of your images are in the same folder, sort them by FILE NAME

Lightroom Sort by File NameLightroom Sort by File Name

• Now all of your images will be separated by File Name.
• This next step is very important.  Now select all of the images that need their time corrected.  To do this click on the very first image in that group and then scroll to the very last image from that camera and hold the SHIFT key to select all of the images that need a time adjustment. NOTE:  It's extremely important that you select the FIRST image first, and work toward the last image for this to work correctly. 
• Next go to the Metadata Menu and select EDIT CAPTURE TIME. 

Change and update the correct time to your images in LightroomChange and update the correct time to your images in Lightroom

• A window will pop up where you need to enter the accurate time under NEW TIME.  The original (and presumably incorrect time) will be on top.
• Once you are ABSOLUTELY sure that you have everything accurate you can click CHANGE ALL.  Once you have done this it CANNOT be undone, so be sure to double check all of your work.

RESULT

Of course it is best to always set your camera clock before every session.  Failure to do so will result in a bit of maneuvering like the instructions above so it's not impossible, only more work, to fix it in post-production.