How to use 'hardly' correctly

As 'hardly' has negative connotation, it is wrong to use it with modals in the negative. The following sentence is wrong:

I can't hardly wait for him.

Look at how 'hardly' is used in the following sentences with their meanings in brackets.

1 The asthmatic baby could hardly breathe. (The asthmatic baby could not breathe.)

2 I hardly have the time to read a book. (I don't have the time to read a book.)