ਕਵਣ, ਕਵਣੁ, ਕਵਣਿ

ਕਵਣੁ ਸੁ ਵੇਲਾ ਵਖਤੁ ਕਵਣੁ ਕਵਣ ਥਿਤਿ ਕਵਣੁ ਵਾਰੁ ॥
ਕਵਣਿ ਸਿ ਰੁਤੀ ਮਾਹੁ ਕਵਣੁ ਜਿਤੁ ਹੋਆ ਆਕਾਰੁ ॥

ਕਵਣ here is a visheshan and will have a aunkar under the ਣ depending if the noun next to it is masculine or feminine. What I want to know what grammar rule is making the ਕਵਣਿ next to ਰੁਤੀ have a Sihaari? what does the sihaari here mean?

ਕਵਣੁ ਸੁ ਵੇਲਾ ਵਖਤੁ ਕਵਣੁ ਕਵਣ ਥਿਤਿ ਕਵਣੁ ਵਾਰੁ
ਕਵਣਿ ਸਿ ਰੁਤੀ ਮਾਹੁ ਕਵਣੁ ਜਿਤੁ ਹੋਆ ਆਕਾਰੁ

Here, the adjective is ਕਵਣ. Since the noun that its describing is ਵੇਲਾ, there is an aunkaR on ਕਵਣ because it is describing a singular male noun.

The next ਕਵਣ also has an aunkaR, because the noun it is describing “ਵਖਤੁ “ is a singular male noun.
Next, “ਕਵਣ ਥਿਤਿ”, ਥਿਤਿ is a female word, so there is no aunkaR on ਕਵਣ
“ਕਵਣੁ ਵਾਰੁ”, ਵਾਰੁ is a singular male noun, so there is an aunkaR on ਕਵਣੁ.

Then to answer your question, ਕਵਣਿ ਸਿ ਰੁਤੀ, I think ਰੁਤੀ here is the bahu bachan (plural) word for ਰੁਤ so that is why ਕਵਣਿ is spelt with a siharee. "ਕਿਹੜੀਆਂ ਉਹ ਰੁਤਾਂ ਸਨ"

Next, ਮਾਹੁ ਕਵਣੁ, ਮਾਹੁ is a singular male noun, so there is an aunkaR on ਕਵਣੁ

ਕਿਹੜੀਆਂ ਉਹ ਰੁਤਾਂ ਸਨ ?

That is convincing. That is plural word, so should also be prounounced with BINDI after bihari.
What were those seasons?

Thank you Gurman Singh Jee. I now understand