The righteous have found various ways to determine when special blessed days in the Islamic calendar occur.* Often these methods are mathematical in nature probably owing to the numerological significance of the Arabic alphabet or astronomical in nature owing to astronomy’s importance in the Qur’an. I too have come across a method of my own which is that on these blessed days one will encounter new trials or difficulties that are more difficult than what you are used to.
The basis for my conclusion is a story of one of the awliya, where he was shown how in one year Allah rejected the Hajj of every pilgrim. But Allah accepted them by virtue of a man that gave up his life savings for making Hajj to a poor lady to care for her children. Though the man didn’t make Hajj, his Hajj was accepted and the wali was told to inform the man that Allah had accepted from him. Hajj is about sacrifice especially the sacrifice of Ibrahim alayhi salam, and so the man’s actions were perhaps closer to the spirit of Hajj than those of other pilgrims. From this I understood, the plain worship may not be what Allah wants from you, but He may send something different to try you upon special occasions, so be prepared.
This may or may not be completely true for everybody but in my experience it certainly was. The 15th of Shaban is a day one should fast upon, but I decided not to fast this day but ended up going hungry at a dinner party (only snacks were served) which tried my patience since I hadn’t eaten since breakfast. On Laylatul Bara of Rajab, my grandfather passed away, may Allah show him mercy. On Laylatul Qadr last week (23rd of Ramadan for those who noticed how the sun rose the following morning without rays as indicated in hadith) I prayed only part of the night and fell asleep early due to the trial of praying near an exceptionally comfortable mattress (sleep on an uncomfortable bed as often as you can). On the night of Eid, a night wherein duas are answered and in which prayer is important, I again found myself too tired and exhausted though I usually have little trouble praying a portion of the night.
These may seem like small problems, but they are big in relation to how they distract one away from the meritorious rewards of these occasions. I can’t necessarily blame it on shaytan, but perhaps its my nafs pushing me away, that if I were to achieve the full success of these occasions, I would then as a result become harder on my nafs, or perhaps its simply a secret of Divine decree, that the reward is great because it is more difficult to worship at that time.
Allah knows best.
*As-Sufuri said (may Allah have mercy on him):
“I saw it written with my father’s hand from Shaykh Abul-Hasan Ash-Shadhili: “Since I reached puberty I never missed seeing Laylatul-Qadr. If the first day of Ramadan is a Sunday, it falls on the 29th; if it is a Monday, it falls on the 21st; if it is a Tuesday, it falls on the 27th; if it is a Wednesday, it falls on the 29th like Sunday; if it is a Thursday, it falls on the 25th; if it is a Friday, it falls on the 27th like Tuesday; if it is a Saturday, it falls on the 23rd, and Allah knows best.”
(Nuzhat Al-Majalis Wa Munkhatab An-Nafa’is” by Al-‘Allama Ash-Shaykh ‘Abdur Rahman As-Sufuri Ash-Shafi’i)