By "present" i understand you mean stationing in peace time. There were obviously many times foreign troops entered the Commonwealth for military campaigns or possibly raiding. Sometimes it's not even obvious whether we talk about stationing or campaigning as 18th century Commonwealth was sometimes called "Open Inn", throughout which the foreign troops moved and stayed at their own will and pleasure.
Silent Sejm, 1717
During the Northern war August II angered enough of the Szlachta to form Tarnogród Confederation which invited the Russian tsar Peter the Great in 1715 to bring his troops "for peacekeeping and mediation". The mediation effort included calling of the infamous Silent Sejm in 1717. The Russian troops remained for another two years and left in 1719.
So they stayed for about four years total. More importantly the Commonwealth lost it's independence in all but name and became Russian protectorate until it's dissolution through the Partitions 1772–1795. Even without the troops physically present, the Russian ambassadors became a de-facto governors of the conquered country.
War of the Polish Succession, 1733–35
After the death of August II the Commonwealth had double election again, with his son August III and his original rival Stanislaw Leszczynski both announced kings by opposing factions. It sparked the War of the Polish Succession with Russian forces participating. They entered in 1733. They were not disturbed during their march back from France in 1735. It's not clear when they left for good.
Seven Years' War, 1756–1763
Russian troops entered again during the Seven Years' War, in which the Commonwealth did not officially participate. So in a sense they were stationed in a vassal state for the purpose of fighting a third party (Prussia). Russia maintained military bases and magazines in the Commonwealth's territory.
The last election, 1764
Russian troops were definitely present during the election of Stanisław August Poniatowski in 1764. Their presence led to the Bar Confederation and the first partition in 1772. The Russian troops remained at least until the Partition Sejm in 1773–1775.
That's about eleven years.
The End, 1792–1795
Enacting the May Constitution by the Commonwealth under Prussian inspiration, was perceived by Russia as an attempt to end the protectorate, and prompted the invasion in 1792, the Second and Third Partition and the end of the Commonwealth in 1795.
So that's about three years of irregular fighting and occupation.
Summary
Polish-Lithuanian Commonwealth in 18th century was a de-facto Russian protectorate, since the Northern War, slowly losing it's independence piece-by-piece. But most of the time the Russian troops did not have to station in it's territory. It was probably about twenty years in total, that they stationed or operated within the Commonwealth borders.
During the reign of August III, the Saxon troops were also a de-facto arm of Russian Empire, as he was neither willing nor able to conduct an independent politics.
Stanislaw Poniatowski is often singled out as Russian puppet, although I'm not sure why as he was not much different from August III in this respect.
The presence of Russian diplomats corrupting the magnates was enough to keep the Commonwealth in the state of anarchy and subjugation. Thus the private Magnate armies were also in a sense funded by Russia indirectly, and could be counted on, to some extent at least, to project Russian power.
The problem was not so much the actual presence of the foreign troops but the fact they could enter and stay at any point, without any realistic chance of preventing them from doing so.
