depending on the breed and sex of the calf, she may hang on to it a while longer...
Here is what I notice for gestation times in my herd (shorthorn/saler/gelbvieh crosses)
Average time is 288 days
very rare before 275 days
never had one over 295 days (that I know of )
first timers are usually 2 days early from average
bull calves will be about 3 days later than heifer calves
I don't know how many days gestation you're figuring with, but be ready for it any time by the sounds of it.