For this salmon marinade in particular, we suggest 30 minutes to an hour as it's acid based. Any longer than that and you risk the salmon becoming mushy after breaking down from the acidity. Depending on the type of marinade you use, you can marinate salmon for anywhere between 30 minutes to 24 hours. For other marinades that aren't acid-based, it's safe to marinate for 12-24 hours in the refrigerator.