I had an accident with the condom one day after my period had finished.

Yes there's a chance. With an irregular cycle I always suggest the other emergency pill called Ella (Ulipristal Acetate). It is the only emergency contraceptive pill proven can prevent pregnancy during the 24 hours around ovulation (You can see that on the Manufacturer's website).

When you have an irregular cycle, you don't tend to know what is a true period, & what is breakthrough bleeding, & don't tend to know when you're fertile.

Overall, it sounds like chances of pregnancy are low. It's probably the Plan B causing the delay.

There are ways to prevent condoms splitting. Its worth researching. For example, nipping a couple of centimetres shut at the tip, as you roll it onto the penis, ensuring no air gets trapped inside. This leaves an air-free pouch for him to ejaculate into.