Lease Says Pay Rent On Or Before The 1st Or The 15th. Does This Mean I Can Pay Anytime Within That Window?

For context (Upstate NY, USA), I have been begging my landlord to fix the heating in my the bedroom of my apartment for over a month. They have not fixed it, but provided me with a space heater. A city inspection will occur soon, but due to the warranty of habitability I believe I have just cause to withhold rent, which I informed my landlord of and they said I will be penalized if I do so. I’m just wondering based on the following wording from my lease, at what point rent will be considered late.

“The total rent for the above premises shall be $$$, to be paid in equal monthly installments on or before the 1st or the 15th of the month that they cover. Should the term begin on a day later than the 1st or the 15th, rent shall be due nevertheless on or before the 1st or the 15th. Payments shall be considered timely if they are delivered or postmarked on or before the due date. The amount of each monthly installment is $$$. If the installment or any portion thereof is untimely, the tenant shall add $70.00 (seventy dollars) as additional rent to the installment.”