Having a long LP doesn't affect your ability to conceive. It cause you to misjudge the OPK testing period though.
For example, if you have a 30-day cycle, the instruction will tell you to start testing on day 12 (30/2-3=12). This is based on the assumption that you have a standard LP, which is half length of your entire cycle. You suppose to expect ovulation on day 15. However if you have a long LP, lets say 18 days instead of 15 days. You will have already O'd on day12. By the time you start OPK testing, the LH surge is long gone. you will probably wonder why all tests are negative, yet you still have your period? did you O? was the test faulty? In fact you have totally missed the window opportunity for testing due to a longer than average Luteal Phase.
So if after a few rounds, you don't seem to be able to detect the ovulation at all, don't panic. Try extend the testing period at the start, try start testing a little earlier than instructed, like test on day 9 instead of day 12. See how does that go.