The example you gave above is a slightly different use of the word 'for'. In this case, 'for' refers to the TOTAL duration of a stay. With this meaning - when you're saying how long a holiday is, for example - you can use any tense that's appropriate. For example : past ( I visited my parents for a few days last month), present simple ( We always visit my parents for a few days every year) or future (We're going to visit my parents for a few days next week). The rule you are talking about only applies to 'for' when it's talking about a period UP TO NOW : in other words, when it replaces the word 'since' because it's describing the length of time that's passed rather than the point at which a situation or activity started. Here are some examples: I've worked here since 2008 = I've worked here for ten years Here's another example to illustrate the difference. Let's say I'm spending a year in Taiwan - the whole of 2018. I arrived in Taiwan in January and I'm going to leave in December. It's now June. You might meet me in Taiwan and ask one of two questions. You: How long are you staying here? Me: I'm staying here for a year . [ Jan - Dec. This is the total duration of my stay - we can use any tense here] or You: How long have you been here? Me: I've been here for six months now. [ Jan --> now. This is how long I've been here so far - we have to use a present perfect because it refers to the period leading up to the present moment] I hope that all makes sense.

Hi Aina, "for" can be used with the present continuous, the sentence you provided is therefore correct. As Anton said, "for" is used when a period of time follows, e.g. do something for 5 days/ for 2 minutes, a week/ a month, etc. You can say "I ride a bike every day for 2 hours" but also "I've been riding a bike for 2 hours" or "I was riding a bike for 2 hours", etc.

for with the period of time since with the moment in the past

Here's reference→https://goo.gl/cKwJuR Please see the first take note. And here're examples about how to use for, which they post on Twitter. →https://goo.gl/8oZ4Lx

for with the period of time since with the moment in the past