When can I say "I use this daily" or "I use this every day"? What about hourly?
Is it correct to say "I will send this hourly"? It seems incorrect, to me.
Daily, hourly, yearly and the like all started as adjectives, but centuries of use license their use as adverbs, too.
OKI will update this report hourly.
This makes some people uncomfortable, however; so you would probably do better to use them only as adjectives and employ the every construction when you want an adverbial:
OKI will update this report every hour.
What you will often see those uncomfortable people substituting is this construction:
?!I will update this report on an hourly basis.
I implore you not to emulate this pompous and awkward workaround.
"I use this daily" and "I use this every day" mean pretty much the same thing.
In some contexts, either one could mean exactly once per day, or an unspecified number of times per day. Like if your doctor said, "Take this medicine daily", that would be understood to mean one pill per day. Or if you said, "We update the customer file every day", that would normally be understood to mean once per day. But if you said, "I drink coffee daily" or "I drink coffee every day", that wouldn't necessarily mean just one cup per day, but rather at least one cup every day.
If you said, "I will send this hourly", that means you will send it every hour. So if you send the first one at 9:00, you'll send another at 10:00, another at 11:00, etc.
Daily is kind of formal version of every day.
Every Day ususally is used when you speak, while daily is used in writing.