Is specialist callback available 24 hours?

[DDollar]

No.  They are available from 5am to 9pm Pacific through April 14, and from 5am to midnight on April 15.

See this TurboTax support FAQ for a contact link and hours of operation - https://ttlc.intuit.com/questions/1899263-what-is-the-turbotax-phone-number

To contact TurboTax customer service/support use their contact website during business hours.  If the problem concerns any type of refund for fees, use the key words billing issues and do Not use the word Refund or you will get a phone number for tax refunds.

Submit your question/problem during business hours and then use the option for Call (a phone number will be provided for Call) to speak directly with a TurboTax agent -

https://support.turbotax.intuit.com/contact/ 

Note:  The Call option will not be available when TurboTax Support is closed.