We’ve moved the two hour downtime that was scheduled earlier this week. It will be on Sunday from 6-8p instead. During this downtime we’ll be upgrading our database hardware which unfortunately can’t be done while the site is online.
In the past, we’ve not done as good a job at giving advance notice when we need to bring the site down. Whenever possible, we will try to give 24 hours notice from now on (usually via a notice on your Twitter homepage).
Of course, avoiding downtime at all is the bigger goal. Scheduled maintenance, like the one this Sunday, will help Twitter to run more smoothly.