Geography is against this:
As you can see, Czechoslovakia stabs deep into the heart of Germany; a move against Poland without taking Czechoslovakia first would leave Germany dangerously vulnerable to attack deep within its flanks, even after the Anschluss. The Polish German border is also significantly shorter than it was after Czechoslovakia was swallowed up by the Reich. In addition to which, the Czech armaments industry was the largest in Europe; a far too inviting a prize to pass up.
And Hitler always went after the weakest party, singling them out, isolating them from potential allies and then attacking, often with the aid of those who would shortly become his next victims; it was the method he employed to take over the Nazi party and then Germany before applying it to foreign expansion; hence Austria, then Czechoslovakia, and Lithuania, and then Poland.
Of course that works both ways. Czechosolvakia does thrust into Southern Germany but likewise it is surrounded by Germany.
A military action against Czechoslovakia would not be significantly more difficult than Poland, even with the Sudeten forts (especially if Hungary - and Poland - joins in too to enforce their own claims).
So the TL might work something like this
May 1938 Hitler orders plans for invasion of Poland
August September 1938 German troops mass on Polish border
September 28 Ultimatum to Poland to give up the Polish Corridor
September 29 Munich Conference
September 30 Munich agreement and collapse of Polish Government
March 1939 Hitler demands Sudetenland
April 1939 Czechoslovakia refuses, France (and Britain) provide guarantees to Czechoslovakia
May 1939 WW2 - Germany declares war on Czechoslovakia, Poland and Hungary occupy their respective sectors of Czechoslovakia after a couple of weeks citing security / protectorate issues
June 1939 Phony war, Fall of Prague end of Czech resistance
July-August 1939 Modified Ribbentrop pact defining Moscow / Berlin / Warsaw influence in Romania, Finland and Baltic states