The satellites will lift off from Satish Dhawan Space Centre in the spaceport of Sriharikota at 6pm.
The 59-hour-countdown begun at 7am on December 14.
"Yes countdown is progressing normally," an official said.
ISRO said the filling of propellant in PS4 stage (fourth stage) were completed.
ISRO would launch the six satellites into a 550 km circular orbit inclined at 15 degrees to the equator. It is using its trusted workhorse PSLV which is on its 32nd flight in 'core-alone' configuration without the use of solid strap-on motors.
Of the six satellites, TeLEOS-1 is the primary satellite weighing 400 kgs whereas the other five satellites include two micro-satellites and three nano-satellites.
TeLEOS-1 is the first Singapore commercial earth observation satellite.It would be launched into a low Earth orbit for "remote sensing" applications.
Antrix Corporation Ltd, the commercial arm of ISRO, has provided launch services in PSLV for 51 customer satellites from 20 countries so far.