There is no conversion between erlangs and minutes.
Erlang is defined as the period of time it takes to keep a traffic sensitive facility busy for a period of time. That period of time has to be used througout your formulae.
The period of time that most folks use is 3600 seconds or 1 hour.
I really am not sure what you are trying to achieve here.
Regarding your previous posts: Erlang B defines the blocking probablility assuming a random call arrival, lost calls cleared from the system, an infinite number of sources and hold times are exponentially distributed.
This would mean that all blocked calls could go to an overflow trunk group. If you were to model an overflow trunk group, that would look more like a peaked call arrival and you would have to make assumptions about the rest. EART/EARC or Neal-Wilkerson traffic models would apply.
If you were assuming that the trunk group you are creating would have both characteristics of handling a regular call load plus overflow traffic you would have to apply both call models and assume that the erlang B model is the baseline with EART/EARC as the additional trunks needed to handle the overflow.