Hey, here’s my experience with it.
Generally, a seed cracks within 2 to 5 days. However, some older seeds or those with a very hard shell can take up to 10, even 14 days.
The 3 factors to check immediately:
Temperature: This is the number 1 factor. Seeds need warmth (between 21°C and 26°C). If they are too cool (below 18°C), the metabolism stops and they will never germinate.
Humidity: The medium (paper towel or soil) should be moist but not soaked. Too much water "drowns" the seed and causes mold before it even opens.
Darkness: Make sure they are in complete darkness.
Wait another 3 to 4 days: If the heat conditions are good, give them a little more chance.
Check the state (with caution): If you are using the paper towel method, gently lift the paper. If the seed has become all mushy or smells bad, it has probably rotted.
My advice:
Give them up to 10 days in total. If nothing has happened by then, it’s likely that the seeds are defective or that they got too cold/too much water. I hope I could help you. Have a great day!