Let's say that your time value is in cell A1
then in A2
you can put:
=A1*1000*60*60*24
or simply:
=A1*86400000
What I am doing is taking the decimal value of the time and multiply it by 1000 (milliseconds) and 60 (seconds) and 60 (minutes) and 24 (hours).
You will then need to format cell A2
as General for it to be in milliseconds format.
If your time is a text value then use:
=TIMEVALUE(A1)*86400000
UPDATE
Per @dandfra's comment this solution may not work in the Italian version of Excel.
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…