I am concreting a 500mm x 500mm section reinforced concrete beam with an span clear span of 3m between RC columns. How many days it would take before stripping the side forms and the soffit forms?
Sounds like the beam will be supported (underneath) by falsework until the concrete has time to come up to acceptable strength. If this is true, there are two concerns about the sides:
1. Damage to the concrete during the form stripping process.
2. Continued curing of the concrete, after the side forms are removed.
Curing is typically continued for a total of 7 days, or so. After removal of side forms curing MAY be handled by using wet burlap, water spray, curing compound, etc.
A reasonable compromise on the damage aspect is to remove the side forms two or three days after concrete placement (this time span is dependent on ambient temperature of course).
Unless you have a VERY pressing need to reuse the side forms, it is probably best to leave things alone until the total curing time has elapsed.