If you’re following a good program then I’d say two days a week is enough. With two days a week you can absolutely make good progress. But what’s more important is that you're training towards failure and your program fits your lifestyle. For instance, whether someone was doing two days a week or five days a week, I would give them a similar amount of volume, but I would just spread it over either two or five days. They wouldn’t necessarily be doing more or less, it would just mean it’s more spread out or more concentrated.