I added a new web product to my GlobalTill store. Do I have to wait for the overnight sync to see it in Shopify?
No. To sync a new web product to Shopify immediately, go to the Web Data tab, select Shopify Sync - Full Update. Otherwise, the product will not be in Shopify until the following day, after the scheduled data sync.
For more information, see the article Can I sync all product and inventory data to Shopify without waiting for regular syncing?