what time should i go to bed? for how long?

right. on saturday morning i start a new shift at work, which is 6am - 6pm. ive had all this week off and have been going to bed at 2-3am.
would it be more beneficial for me to go to bed tonight (thursday) as late as physically possible and waking up early so ill be tired for an early night on friday or go to bed as early as possible and wake up early?
which will be easier for me to get up and let me last the 12hr shift?