How to explain my availability for a job?

I know this sounds like an easy no brainer question but I got a call kind of late so I didnt answer from a job I had an interview for this week and they left a message asking me for my availability so they can offer me something. I plan to call back and say I am available anytime but I feel like they would want me to be more specific so should I ask what the shifts are and how long they are? Or how should i ask it?

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