Missed combined oral contraceptives
The maximum interval between COC pills is 48 hours, therefore a COC is not considered 'missed' until it is more than 24 hours late. The 'riskiest' time to miss a pill is in the first 7 days after the hormone-free interval (inactive pills), when the chance of breakthrough ovulation is highest.
[NB1] [NB2] [NB3]

NB1: This advice applies to combined oral contraceptives, and to progestogen-only pills (POPs) containing drospirenone (eg Slinda). Product information may differ from this for some formulations.
NB2: This advice does not apply if more than four pills have been missed. Seek medical advice if five or more pills have been missed.
NB3: These instructions do not apply to quadriphasic combined oral contraceptive pills (eg Qlaira). See the product information for advice.
NB4: Ulipristal (another type of emergency contraception) is usually not suitable in this scenario; if any hormonal contraception (excluding levonorgestrel-releasing intrauterine contraceptive devices) has been used in the past week, it may reduce the effectiveness of ulipristal. The contraceptive pill also can't be restarted for 5 days after ulipristal, so condoms are required for 12 days after taking ulipristal.
Adapted with permission from: Contraception: an Australian clinical practice handbook. 4th ed. Ashfield, New South Wales: Family Planning New South Wales, Family Planning Victoria, and True Relationships and Reproductive Health; 2016.