Hi Sergey, I'm doing this also, and don't get exact results or else I'm misunderstanding something here. Is something wrong with the rounding? From your example, try this:

clear
Store DATETIME() TO datetime1
? datetime1
WAIT WINDOW "Waiting 5 seconds" TIMEOUT 5
Store DATETIME() TO datetime2
? datetime2
lnSeconds = ROUND( datetime1 - datetime2, 0)
? lnSeconds
lndiff=SecToTime(lnSeconds)
?lndiff
? "shouldn't it return 0:00:05, not 0:59:55?"

FUNCTION SecToTime
* Convert seconds to the Time string
PARAM nSeconds
LOCAL cHH, nTm, cMM, cSec, cTime, i
cHH = ALLT(STR(INT(nSeconds / 3600)))
nTm = nSeconds % 3600
cMM = PADL(INT(nTm / 60), 2, "0")
cSec = PADL(MOD(nTm, 60), 2, "0")
cTime = cHH + ":" + cMM + ":" + cSec
RETURN cTime

TIA,
Tracy