Is anything showing at all
If no timer shows anywhere, the app embed is almost always off in your live theme. The app Home shows its status with a button to turn it on. Turning it on in a draft or a copy does not count, since each theme has its own switch.
Is the timer running right now
Published is not the same as running. A timer with a scheduled start in the future stays out of sight until then. A recurring timer shows only inside its window. A countdown to a date set to unpublish has gone at zero. A fixed minutes timer set to hide has gone for a shopper who reached zero, and a shopper who closed a bar does not see it again in that browser.
A save reaches the storefront after a short delay, so reload the page once if you have just published.
Does this page match
Check the timer placement and exclusions against the page you are on. Then check whether another timer of the same type wins on this page, since one product timer, one bar, and one landing timer show per page. Then check countries, if the timer targets some. A cart timer shows only while the cart has items.
A timer set to Custom position shows only inside an app block that holds its Timer ID. If no block has it, it shows nowhere.