Both tends to make people think you're more important and worth more, not usually make them strike you off their list and move on to the next person.
The exception would be really low level positions where they see people as interchangeable, but even then in most cases people have already mentally chosen you when they call, and not being available makes you more desirable, not less, so for them to move on they need to have cared very little to begin with.
... which is another reason to not be instantly available - I for one don't want to work for people who see little enough value in me to be prepared to drop me if I don't answer the phone 24/7 unless I've been contracted specifically to be available at any time (and you better believe they'll pay through the nose for that).
A lot of younger employees could do with learning to set boundaries, be unavailable and say "no", and experience how that can often get them a lot more respect and better job conditions.
It's not if you're offering a contract with shitty fishhooks designed to fuck over anyone who hasn't had a good lawyer spend some time looking over the contract - then it's a very rational ploy, with the side-effect of checking how easy it is to bully a potential hire into acting against their own best interests.
What you as an employee should think about that is left as an exercise for the reader.
If I was a good hire yesterday, am I a good hire today?
I like to ignore offer deadlines. I just don't understand them.