Twitter Blog: Down Time Rescheduled:

A critical network upgrade must be performed to ensure continued operation of Twitter. In coordination with Twitter, our network host had planned this upgrade for tonight. However, our network partners at NTT America recognize the role Twitter is currently playing as an important communication tool in Iran. Tonight's planned maintenance has been rescheduled to tomorrow between 2-3p PST (1:30a in Iran).

I have to admit in my 17 some years in the admin business I have never had to reschedule any kind of system update due to political unrest.