Could you come now? (present tense expressing a polite request)
No, I can come tomorrow. (future tense, expressing ability).
Your example sentence is in the present perfect tense because of the structure “I have released” Here ‘could’ is used as an auxiliary modal verb to change mood of the sentence to express possibility.
I could have the deposit released within a few days, but there was some delay due to reasons beyond my control.
If I had the necessary funds in my account, I could have the deposit released within a few days.
To be sure about the tense; please see; YouTube - Perfect Modal Verbs
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