Countdown timers are a great way to create urgency on donation pages especially around appeals. However, you may only want to include this at a later date e.g. the last week of the campaign.
You will need to use the advanced template for this
You will see something that looks like this
1. Click on the right most widget
2. Select a date which has already passed
3. Tick the box which says "Hide Countdown timer when reach goal"
3. Remember to publish the page once completed
You can bring the live thermometer bar back at any time by then selecting a date in the future and pushing publish