Answer:
Days or years before the major earthquake.
Step-by-step explanation:
The foreshocks always come before the major earthquake. They can appear only a single day before it, weeks, months, or even years. It is a nice indicator that something bigger is coming, so if people are wary enough they can avoid the devastating effects of the major seismic activity afterwards.
For example, we can take the foreshocks and the major earthquake in Ohrid, Republic of Macedonia, in the summer of 2016, where the foreshocks started about two months earlier, and they were present every day for those two months, slightly increasing in intensity, until the major earthquake of 6.9 magnitude according to the Richter scale came.
Glad I could help!!