As per wiki article on Muchukunda:
Then Indra said to the king Muchukunda, "O king, we, the Devas are indebted to you for the help and protection which you have given us, by sacrificing your own family life. Here in the heaven, one second equals one year of the earth and you had fought with asuras for one year of heaven. Since, it has been a long time, there is no sign of your kingdom and family because it has been destroyed with the passage of time. We are happy and pleased with you, so ask for any boon except Moksha (liberation) because Moksha (liberation) is beyond our capacities".
So it is clear that 1 second of heaven is equal to 1 year of of the earth. Now when Arjuna went to heaven to meet his father Indra for divyastra after doing penance, it must have taken some time to receive divyashtra, because this part of story also includes curse of Urvashi.
But if we notice bold part in above quoted text, based on that equation, this raises a question that how much time it took for Arjuna to complete receiving divyastra because if he gets any late it would already cross more than 12-13 years and then the consecutive story would not make any sense.
So my question is does time lapse differently during Arjuna visit or did whole story complete very fast like in few seconds?
