[TZubiri]

1. 24 hours is not common at all for A records, it should be between 5 minutes to 60 minutes.

Perhaps you are thinking of NS records, which would only be changed very infrequently, and both the source and target systems should be up so that there's no loss of availability.

2. Never had that, it's more likely that you did something wrong rather it being an ISP issue.

Feel free to send me an email with specifics, the email is in my profile although in a cryptic format to avoid spam.