Ther are several factors,therefore no definitive answer.
Depends on a) Writer speed b) DVD Rom speed if separate and copying direct from another disc rather than doing a backup etc.
Also if system discs usd are DVD+/DVD- /DVD Ram.
For example, using a 16 speed DVD Rom copying to current spec DVD writer should take 20 -30 mins for 4.7Gb of data, backing up data from your H/d direct ,should be somewhat quicker.
Ep, glad to see you come back and tidy up...did want to ask a one day favor, I want to enhance my resume , was hoping you could make me administrator for a day, if so, take me right off since I won't be here to do anything, and don't know the slightest about the board, but it would be nice putting "served administrator osnn", if can do, THANKS