Gym instructor Vinay Sharma and bus cleaner Akshay Kumar Singh, along with two others, were convicted last year over the December 2012 attack.
In March, the Supreme Court put on hold the execution of two others convicted in the case - fruit-seller Pawan Gupta and unemployed Mukesh Singh - while they appealed.
It is not unusual for legal cases to drag on for years in India after convicts start the appeal process.
The victim, who worked in a call centre while she studied, became a symbol of the daily dangers women face in a country where a rape is reported on average every 21 minutes and acid attacks and incidents of molestation are common.
A fifth defendant hanged himself in his cell.