Maria has a cycle length of 29 days and her menstrual bleeding starts on 4th of March. To determine the period of her ovulation, she must start testing on the 12th Day from the beginning of the cycle, i.e. on the 15th of March.
Maria should register results using the urine strips on the 15th, 16th, 17th, 18th and 19th of March.
If the test is negative on the 15th, 16th, 17th and 18th and a positive result on the 19th, then the most convenient time for conception is 20th-21st of March.