The differences between 9:30 pm and 9.30pm might seem irrelevant, but these small choices give character to the words presented by people and organistions.
People notice these tiny decisions. Like the colon and spacing in 9:30 pm, they can convey formality, order and tone.
Inconsistent stylistic choices read sloppy and weak; even if a reader doesn’t consciously notice inconsistencies in a text, they will likely sense that the writing lacks control.
Writing which is inconsistent reads like unprofessional writing. When in doubt, make a choice; then stick to it.