The contacts can be synced to Salesforce from the Xero app automatically at a preferred time by creating a scheduler in your org.

To generate the scheduler, click on Setup, and search for the Apex classes button. Then click Schedule Apex, and enter the job name. Select the "XeroContact" in the Apex Class field and enter the frequency details, Start date, End Date, preferred time, and Save it.

The scheduler is executed at the time set in the preferred time in the scheduler and the Contacts created in the Xero app are synced to Salesforce automatically and are shown in the Xero Contacts tab.