The time for appeal is limited. However there are other mechanism that can be exercised so long as he is under "custody" including prole or probation period. You need to give more fact regarding his conviction and sentencing. His case needs to be reviewed by an attorney to see if there are issues that can assist you in pursuing your goal.
The time to file a notice of appeal is within 60 days of sentencing, PERIOD. This is jurisdictional. However, there are other "appellate" remedies that are not time limited, although they typically have other restrictions. A habeas corpus petition can be filed if there is evidence that the imprisonment is unwarranted. This can be due to newly discovered evidence, etc. A writ of error coram nobis is another appellate vehicle. You need to talk to a qualified appellate lawyer about the specifics of your situation to find out if there are any avenues still open.
The opinions rendered herein are based on general principles of law. Laws vary from jurisdiction to jurisdiction and there are often numerous factors which can render advice or an opinion inapplicable. You should NOT make any decisions about the handling of a legal matter without first directly consulting with an attorney about the particulars of your case.