We have all heard about the Challenger disaster.

Reading the Vehicle breakup subsection, this sentence made me very curious:

The external tank at this point suffered a complete structural failure, the LH2 and LOX tanks rupturing, mixing, and igniting, creating a fireball that enveloped the whole stack.

I know it is not the explosion which destroyed the whole vehicle but aerodynamic forces, but I wonder:

• how many liquid fuel and oxydizer were left in the external tank at the time of its destruction?

Bonus question:

• how many second were left before SRBs separation?

I couldn't find any information, so thank you for your answers!