Two calendar days and forty-eight elapsed hours are not always identical.
Calendar span
Monday morning through Tuesday afternoon touches two dates but lasts less than forty-eight hours.
Elapsed duration
Forty-eight hours from Monday at 3 p.m. ends Wednesday at 3 p.m.
Best practice
Use exact dates and times when consequences matter.
Frequently asked questions
What does biduous mean?
It means lasting or continuing for two days.
Is biduous a real word?
Yes. It is a rare historical English adjective with Latin roots.
How is it pronounced?
Approximately BID-yoo-us.
Is it the same as dubious?
No. Dubious means doubtful.
Does it always mean forty-eight hours?
No. It can refer to two calendar days.
Can it describe a flower?
Yes. Older dictionary evidence uses it for flowers lasting two days.
Is it common today?
No. Two-day is much more common.
Should it be defined for readers?
Yes, especially outside historical or specialist writing.