When setting writing goals it’s best to set yourself small, manageable chunks. Otherwise, you can be setting yourself up to “fail” if you don’t manage to achieve them, and this will become demotivating, leading to a vicious circle.
What is manageable for you will also vary according to your health, experience, life challenges, workload and so on. For one person, 1000 words a day may be ‘easy’, whereas another person can only manage a weekend session every couple of weeks and struggles to get 250 words onto paper/screen. Or someone might say they are going to write 50,000 words in 3 months whereas another person would be lucky to get a single chapter done. The important thing is to work out what is achievable for you.
Once you can achieve your small scale goal, then consider whether you could stretch it a bit, say, by adding another 250 words into that sporadic session, or making it two chapters. Every word got down on screen or paper is something to work with and is an achievement in itself, especially if you have a lot of odds stacked against you that get in the way of writing.