I'm using the 12 month free EC2 service, But the bill dashboard shows it is counting by hours day by day now.

Hello.

If you are covered by the free tier, your bill will show the usage time and $0 charge as shown in the image below.
There's no problem because you won't actually be charged.
If you actually see a charge greater than $0, such as $1, there is a high possibility that your usage is beyond the free tier, so you will need to investigate your AWS resources.
I think that the 12-month free tier is written as "monthly free tier" on the bill, so if this is written, I think there is basically no problem.

If you want to be alerted in case your AWS costs start enduring costs, create a budget in AWS Budgets.

Take a look at https://docs.aws.amazon.com/cost-management/latest/userguide/budget-templates.html for a template to create a simple budget, to inform you if you're going over your Free tier.

Go to https://console.aws.amazon.com/billing/home#/freetier and it will show what the Free Tier entitlements are for your account currently, as well as how much you have used of each, and a projection of how much you are likely to use for the whole month if you continue at this rate.