what is the validity period of NC-OBC certificate for applying to IPM INDORE (IPMAT)

Any OBC ncl Certificate is valid for 3 years from the month it has been issued. And it can be used for educational and professional purposes. And it is the same format both purposes.

As per 7th pay commision recommendation the Non-creamy OBC certificate validity is one financial year for applying in any governmental institution.

The Non-creamy Layer Certificate would be applicable to OBC candidates who are covered under Income/Wealth Test criterion. The income limit is decided on the basis of income earned during three previous financial yearspreceding the year of appointment. To illustrate, the validity of non-creamy layer certificate issued during any month of the financial year 2016-17 covering 3 preceding financial years viz. 2013-14, 2014-15 and 2015-16 be accepted by the concerned authorities for any appointments or recruitments which would be valid during the period April 2016 to March 2017 ( which is that particular financial year)
If Non-creamy certificate required for getting appointed into State Gov or Central Gov. Generally the validity of NCL for Central Gov. is 1 year.Whereas Validity of NCL for State Gov. is 3 years.

One financial year if you can not understand will be for example from 2018 APRIL to 2019 MARCH. So, to apply for IPM INDORE(IPMAT) your certificate should be of the present financial year. Or else you can renew it.
To do this procedure is same as for the issue of original certificate.You have to your district tahsildar office and with suitable docs like, validity,non creamy layer,I'd proof,address proof,etc only this time you need to take your old certificate in addition and you can renew it