Time limit for filing letter of adm. With will

Mother had life interest in Father's Estate. Took income for 13 years. Mother died in July 2016. Executors refused to file probate in March 2017. Both Witnesess to Will signed affidavits verifying the signatures in March 2017. Some Estate assets are still not traced due to missing original paperwork and difficulty with Banks in last 12 months. Sole, residual beneficiary wants to file petition with the help of a lawyer in Kolkata for Letter of Adm. with Will annexed. Beneficiary can justify the delay in filing by enormous documentary evidence . Q 1 :Is there a time limit for filing the petition for LOA with Will annexed ? If yes, what the time limit for filing ? Q2 : If Estate assets are over 1 crore rupees, which court the petition needs to be filed, Sessions Court or Kolkata High Court ? Clear answers will be appreciated.