You write your availability in a cover letter like this:
‘I’m available to start this position as of [day Month year].’
Only note your availability in your cover letter if the job advert specifies a start date. Otherwise, the employer will verify your availability during a job interview.
Also, you should state your availability towards the end of your cover letter to avoid distracting the reader from your job-relevant experience and skills.
If the employer asks you to specify your daily availability in your cover letter, write:
‘I’m available [Day] to [Day] between [time] and [time].’
Or, if your availability varies from day to day, write it in a bulleted list so it’s easier to read:
- [Day]: [time] to [time]
- And so on