Synchronization of hours between fortigate and my fortiswitch

Hello teams, for two days my network has been off due to a temporary internet outage. After the return, the fortigate was no longer accessible via the mistletoe, I had to go connect to the console to check the reason. To my surprise, the time had gone from UTC -5 to -8. After changing the internet connection came back gradually. But on the other hand, most of my fortiswitches are offline. After investigation I noticed that there was a time difference between the offline fortiswitch and the fortigate. 20 seconds on average. Remember that my fortiswitch are configured in standalone to be managed by my fortigate. Please I really need your help.