In other words if the Japanese army had stood longer, then the Soviet invasion on Poland would have been delayed and might have had an influence on how the Invasion on Poland moved
I would say the end of the Khalkhin-Gol battle and the Soviet entry into former Poland's territories was just a coincidence. Why?
There was nothing to influence on September, 17th, 1939 except the German troops' proximity to Moscow, since Poland had been already defeated
I know, in present day Poland's historiography there are widely accepted statements, that Poland was defeated by the double assault from Germany and the USSR. And had it not been a Soviet "invasion", Poland would have successfully repealed the German assault, since the Germans were starting to experience fuel shortages etc. (this particular "theory" was promoted by Polish historians according to Suvorov-Rezun, he mentioned this in one of his works), but these "theories" are questionable at the very least.
There was no functional government in Poland on Sep. 17th, an assertion which can be found in various sources like Tippelskirch's History of WW2 (in Russian), who stated that the government fled on Sep. 16th or Liddell Hart, who stated it fled on Sep. 18th., other authors (like Kacewicz G.) provided Sep. 17th as the date. For me it makes not much difference whether the Polish government was in Romania already at Sep. 17th or it was somewhere on the Romanian border ready to flee the next day.
The most astonishing thing about the "existence" of the Polish government on September, 17th is the anecdotal story about how the Soviets notified the Polish government about the necessity to enter the former Polish territory.
The Polish ambassador to Moscow Wacław Grzybowski refused to contact the Polish government on a request of Soviet Vice Foreign Minister Potemkin (in Russian, an extraction from the official journal of Vice People's Commissar of Foreign Affairs Potemkin regarding a discourse with Polish ambassador Grzybowski, sent to General Secretary of the VKP(b) Stalin, Sep. 17th, 1939):
the ambassador is refusing to report to the government about the Soviet note, which is trying to excuse this attack with arbitrary statements that Poland has been finally defeated by Germany and that the Polish government does not longer exist
When Potemkin replied that this was out of the ambassador's competence to decide whether to transfer a message from the Soviet government to the Polish one, Grzybowski said that the note should have been delivered via the Soviet embassy in Warsaw, Potemkin responded that there already had been no Soviet ambassador there. Then Grzybowski admitted, that he didn't have communication with the government but kept stating that the government was still in Poland and fully functional. After Potemkin's offer to use Soviet communication channels to deliver the note, the Polish ambassador responded that this (the suggested use of the Soviet channels or assistance) would have been repugnant to "the dignity of the Polish government". Long story short, Potemkin and Molotov were forced to sent a courier to the Polish embassy and to give the note to someone there (probably a doorkeeper) in return for a receipt before the Polish ambassador left Potemkin, lest he forbids the doorkeeper to sign the receipt.
Please note, that this story was taken from a book published by the International Democracy Fund, which had (the fund ceased activity just a couple of weeks ago) a strong affiliation with various Soros and the US government financed entities, so it would be hard to dismiss that as a "communist/Russian propaganda".
So in summary, the Soviet "invasion", the most likely, was motivated by the defeat of Poland, absence of anything, which could somehow impede the German reach further to east and the desire to keep the German troops as far from the main Russian territory as possible. The Barbarossa plan's success could have been much likely to happen, had not Stalin "invaded" Poland.
This opinion was pronounced by Winston Churchill:
On 1 October 1939, Winston Churchill—via the radio—stated:
... That the Russian armies should stand on this line was clearly necessary for the safety of Russia against the Nazi menace. At any rate, the line is there, and an Eastern Front has been created which Nazi Germany does not dare assail. When Herr von Ribbentrop was summoned to Moscow last week it was to learn the fact, and to accept the fact, that the Nazi designs upon the Baltic States and upon the Ukraine must come to a dead stop