υπομονή and υπομονήν is exactly the same thing, the same word. They are forms of the same word. No nuance at all is intended. υπομονή is Nominative Case and υπομονήν is Accusative Case.
The same happens with τέλειον and τέλειοι. They are forms of the same adjective. The first one is neuter singular (Nominative or Accusative) and the second one is masculine Nominative Plural.
In ancient Greek we have various endings for the same word depending on the gender (masculine, feminine or neuter), depending on the case (Nominative / Genitive / Dative / Accusative / Vocative) and depending on the number (Singular or Plural).