When to start testing ????

Theresa • Married for 3 years, Cat Mom of 10 and an all cat Veterinarian, TTC baby #1 for over 1 year..... ♥️♥️

I just finished my period this morning , is it too early to start OPK strips now ??? Last month my cycle lasted about 40 days and I ovulated at CD25. But could this change from month to month?? This is only my 2nd month of TTC so still learning. Help please !!!