I had the same question, so, using a script I'd written to update the stock data, I wrote a sequence of commands to update AAPL data every minute for ten hours overnight and print the top two lines of the file containing historical data, i.e.
for i in {1..600}; do
../updatedata.py aapl.csv
head -n2 aapl.csv
date
sleep 60
done
The relevant excerpt of the results was:
updating aapl.csv from 2016-01-21 to 2016-1-22
Date,Open,High,Low,Close,Volume,Adj Close
2016-01-21,97.059998,97.879997,94.940002,96.300003,52054500,96.300003
Fri, Jan 22, 2016 8:12:06 PM
updating aapl.csv from 2016-01-21 to 2016-1-22
Date,Open,High,Low,Close,Volume,Adj Close
2016-01-22,98.629997,101.459999,98.370003,101.419998,65562800,101.419998
Fri, Jan 22, 2016 8:13:07 PM
updating aapl.csv from 2016-01-22 to 2016-1-22
Date,Open,High,Low,Close,Volume,Adj Close
2016-01-22,98.629997,101.459999,98.370003,101.419998,65562800,101.419998
Fri, Jan 22, 2016 8:14:08 PM
where times are EST. This particular stock was updated at 8:13 PM EST. I would assume it does take some time to update all the stock data, so perhaps retrieving the data at 9:00:00PM EST would be sufficient.