(free trial) Is there a reset date of 30-day usage during free trial period?

The reset date is typically based on the date when you first signed up for the free trial. So, in your example, if you signed up for the free trial on January 1st and started using EC2 instance on January 20th, then the limit reset date would likely be on February 1st, which is the start of the next billing cycle or monthly period. In your case the free trial will start from the day when you created the AWS Account for the first time till 12 Months (365 Days).