The basic US Army guidance for matters like this is publication FM 3-21.5, Drill and Ceremonies, which is available online in several places. The other armed services have similar guidance.
"Should there be a certain time and place for a Soldier to salute "Old Glory"?"
FM 3-21.5 says:
Military personnel passing an uncased National Color salute at six steps distance and hold the Salute until they have passed six steps beyond it. Similarly, when the uncased Color passes by, they salute when it is six steps away and hold the Salute until it has passed six steps beyond them. NOTE:Small flags carried by individuals, such as those carried by civilian spectators at a parade, are not saluted.
In formation. Individuals in formation do not salute or return salutes except at the command Present, ARMS. The individual in charge salutes and acknowledges salutes for the entire formation.
(("Uncased" means that the flag is unrolled and flying.))
Obviously, this guidance applies in ceremonial situations. A soldier walking by himself past the base flagpole would not normally salute the flag.
There are other special situations in which a salute to the flag is given. Examples are morning and evening colors, and boarding or leaving a Naval ship. These are explained in detail in FM 3-21.5.
"Should a Soldier salute always to our "Star Spangled Banner"?"
I assume that you're talking about the song here. FM 3-21.5 covers that as follows:
c. Outdoors.Whenever and wherever the United States National Anthem, . . .is played, at the first note, all dismounted personnel in uniform and not in formation face the flag (or the music, if the flag is not in view), stand at Attention, and render the prescribed Salute. The position of Salute is held until the last note of the music is sounded. Military personnel not in uniform will stand at Attention (remove headdress, if any, with the right hand), and place the right hand over the heart. Vehicles in motion are brought to a Halt. Persons riding in a passenger car or on a motorcycle dismount and salute. Occupants of other types of military vehicles and buses remain in the vehicle and sit at attention; the individual in charge of each vehicle dismounts and renders the Hand Salute. Tank and armored car commanders salute from the vehicle.
d. Indoors.When the National Anthem is played indoors, officers and enlisted personnel stand at Attention and face the music, or the flag if one is present.
I hope this helps.