very small starter volume , no wonder the yeast is ripping through it but they won't be multiplying much if at all
What is the batch size ?
Calculating starter volumes and cell counts also factors in starter method ie stir pate , intermittent shaking
For my shaken starters on a 23 litre , 1.060 batch i usually build them to 1.5 - 1.8 litres and it's still a borderline underpitch depending which calculator you use .
I do chill and decant off much of the spent beer and pitch yeast cold with very short lag times and strong ferments .
If you want to save half your yeast for next batch then let it ferment out , shake it up and split it into a small sealable jar then build half of it up to the volume you want for this batch
Good news is you have viable yeast
Bad news is you won't have time to build up a big enough starter in 24 hours