Does delaying the recitation of supplications (adhkar) after obligatory prayers affect their merit, such as delaying them to attend a lecture or forgetting them for an hour or more?

The basic principle regarding tasbih (glorification) and the prescribed adhkar (remembrances) after prayers is that they should be recited immediately following the obligatory prayer (Salat al-Maktubah), as indicated by the noble Ahadith, such as the texts of the Hadith (definition) of Thawban and the Hadith of Ka'b ibn 'Ujrah. Sheikh Al-Albani mentioned that these adhkar are to be recited immediately after the obligatory prayer, and that whoever recites them after the Sunnah (definition) prayer has no supporting text and contradicts the Ahadith. If someone forgets or is distracted from these adhkar, but then recites them before a long separation of time, they will attain the full reward. However, if they recite them after a long separation, they will miss the full reward but will still receive the reward for general remembrance. The determination of what constitutes a "long separation" is left to common practice.