Only for Sun transit based events like Sankranti, Ratha Saptami, Sunrise is important. Like Sankranti cannot be celebrated on a day if Sun enters next Rasi after sunrise. Sameway if Saptami tithi starts after sunrise, then next day is Ratha Saptami. This also applies to Ugadi, where Chaitra Padyami starts is before sunrise and for sometime beyond..
Also for birthday (Jayanti), humans and cosmic gods are to be considered differently. For human born like Rama, Krishna, Hanuman etc. Nakshatra is important, not tithi. Chaitra month, Punarvasu nakshatra day for Rama, Sravana month Rohini nakshatra for Krishna, Vaisakha month Poorvabhadra nakshatra for Hanuman.
Rama Navami, Krishna Ashtami are wrong !
For cosmic gods who did not take human birth like Ganapati, Siva etc.. tithi is to be considered. Bhadrapada month Chaturthi/Chaviti (4th) is for Ganapati.
Few have started spreading messages that Jayanti term should only be used for those who took birth and died. For Chiranjeevi like Hanuman, Janmotsav should be used. These ignorants have not read any literature like Parasara Samhita and also perform Hanuman Jayanti on wrong date in April (when Hanuman found seetha in Lanka). This is actually Hanuman Vijayotsav. Parasara used the term 'Hanumajjayanti' in his book and also clearly gave rituals to be followed on that day. But ignorants are using that day to take out processions and dance on roads.