According to the Indian law, 'anybody' file an opposition on trademark, if they trust it is creating confusion in the market. Here 'anybody' alludes to people, partnerships, organizations, firms, and trusts. In the event that at least one individual has a similar concern or issue they can file an opposition on a trademark together.
When the notice of opposition is submitted then you are needed to file a counter-statement within 2 months. In the event that, if you fail to file a counter-statement, the candidate is considered to have abandoned your application
Try not to stress, if you can file proof within a specified time, at that point you can file it later as 'future proof'. Anyway, this should go with an interlocutory allure explaining the clarifications the reason delay in filling of the said proof and mentioning Registrar's approval to neglect the delay.