It doesn't necessarily need to be 7, but it's best to wake her up at the same time everyday. This will give more structure to your day too. Don't worry if she can't go past the 45mins a time. That means her routine will look something like this;
E 7
A
S 7.45-10.00
E 10
A
S 10.45-1.00
E 1.00
A
S 1.45-4.00 etc. etc.
You shoot for a 12hr day, but since your lo is struggling to stay awake for more than 45 you might make bedtime a bit earlier too. To find her ideal bedtime keep moving it forward by 15mins every 3 days, until you find the bedtime which doesn't make her OT. Or else you can go for a slightly longer catnap, as long as it doesn't interfere with her night sleep.
xxx
charm