Because the relationship between the discharge current vs the capacity of secondary-mode rechargeable batteries is nonlinear, the discharge time is difficult to obtain via calculation. Normally suppliers will provide a “Typical Discharge Characteristics” (the graph of Voltage(V) vs Discharge Time(hours)) on their datasheet, such as Panasonic’s HHR-450AB21,
The discharge time is about ~4.6hr (<5hr) in 1.0V.
If you are looking at the discharge time of rechargeable battery, you may need to know that some are designed for high capacity, and some are designed for high power, such as Panasonic’s HHR-70AAAB7,
This battery shows a longer discharge time (> 5 hrs) but less discharge current.