All time low is when the whole market is bleeding hard, in mid 2018 and 2019 most altcoins lose 85% of their value compare to their ATH so I believe ATL aka bear market should be the buying time and ATH aka bull season should be the selling time
and when the momentum hit, my biggest regret was panic selling and not buying back when bitcoin was at its lowest market. hard to believe because of a lot of negative news and I'm not too sure about bitcoin. in fact, we can see a lot of altcoins have really struggled to develop their market.