Using OPK twice a day

Jessica • TTC # 1
I have been using the Clearblue ovulation kit for the past couple of months. The directions say to test with 1 stick every morning. I was wondering if it would be a good idea to test in the evening as well. I have heard of people doing this and getting a negative result in the morning and a positive in the evening or vice versa. Is it possible to ovulate later or earlier in the day? If not I just don't wanna waste the test strips, the kit is kind of expensive.