I do something very similar in my login script but as I have more than 2800 computers,
to be sure that 2 users are not connecting at the same time, I write the results in a
.csv file named with computer name on a centralized share.

When I want to see the information, i have made a .kix script that concatenate all the .csv files in a single .xls file
thus, no conflict possible...
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Christophe