[ז' שבט תשי"ד]
...ומה שכותב שלא ישלוט כו' הנה זה כבר פעם השני' שמזכיר לי ענינים כאלו, וגם אז כתבתי לו דמאן דלא קפיד לא קפדינן עמי' ובפרט בענינים אלו שכיון שאמרו שלא ישאו ביום א' ה"ז גופא שאל"כ הוא אין מקום לחשש כלל וכלל והשי"ת ירבה השמחה במעונו לכאו"א ויעויין רמב"ם סוף הל' לולב הובא במכתב כ"ק מו"ח אדמו"ר שבהקדמת קונטרס העבודה.
[7 Shevat 5714]
...Regarding what you write about not being affected, etc., this is already the second time you mention such matters to me. Even then, I wrote to you that for one who is not particular, we are not particular with him, especially in these matters. Since it was said that they should not marry on Sunday, this itself shows that otherwise there is absolutely no reason for concern at all. May Hashem increase the joy in his dwelling for each and every one. See Rambam at the end of Hilchos Lulav as brought in the letter of my father-in-law the Rebbe in the introduction to Kuntres HaAvodah.
Summary
If a person does not give weight to superstitions or unfounded concerns—especially regarding marriage timing—there is no need to worry about them. The Rebbe encourages focusing on joy and trusting in G‑d's guidance.