I think you need to arrange for a centrifuge with higher 'G', increasing the time won't help.

Agree with Varun Ahuja

If we take "spherical cows in a vaccum" :)) than yes, you just double the time and the impulse will be prserved (impulse=F*t). But in reality if you, say, centrifuge something in a viscous medium or alike -- this medium will just maintain your particles suspended till some force threshold, no matter how long (in reasonable timeframe) you do centrifugation.