There are again more than one versions of this particular Mahamrityunjay Mantra, the common variation is of the word Maharudra being replaced by Mahadev. There is another similar version which is published - Here.
ॐ मृत्युंजय महारुद्र त्राहिमां शरणागतं | जन्म मृत्यु जरा व्याधी पीडितं कर्मबन्धनैः ||
Om Mrityunjay Maharudra Trahimam Sharnagatam | Janmamrityujara Vyadhi Piditam Karmabandhanaih ||
After studying a lot of texts, I have come to the conclusion that this Mahamrityunjay Mantra will bear full results after 33 Lakh Mantra Chants are completed. This may sound extremely difficult, but it must be remembered that this kind of Mantra Sadhana is never wasted and the penance and effort is carried forwards in future births.
I would also advise against counting the number of Mantra Chants.