To get the time when OS/2 booted read the date & time of the swapfile, e.g.
bootTime = stream( 'c:\os2\system\swapper.dat', 'c', 'QUERY DATETIME' )
Please note that the swapfile may be in a different location and that there may be no swapfile at all.
(see also RxUptime - get system uptime information)