Hi Dave!
The “when is right” question is a bit of a “how long is a piece of string” situation - hitting the exact right spot will vary from person to person, often due to prior experience with Welsh.
We recommend not reading because it does a number of things:
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If you have no or little experience of spoken Weslsh, then reading too early will play ahvoc with your accent. There will be lots of words in your vocbulary that you mispronounce, and the vowel sounds will often be pure English, or worse, cod-Welsh. There appears to be a further difficulty that what you learn by reading is taken by the subconscious as fact, whereas what you learn by hearing is more open to change. If you learn a word wrong by reading, in my exoerience, it takes a lot more effort to change it than when you learn a word wrong by hearing it. Odd. but seems to be true!
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Understanding writing is easier than understanding speech, which will give you a false sense of progress. That’s not a problem if you want to read lots, but if you think you’ve got loads of Welsh, but can understand nothing, it will destroy your confidence. Even SSiWers who have done all the listening practices and worked really hard at listening / speaking can take a knock when they first try to use their Welsh, especially if they do that later in the courses, when they’ve learnt so much, but real life Welsh is another step up. For SSiWers who stick at it, it passes quickly, but if you’ve got a lot of your progress from the written word, you mauy have to take a few more steps back when you get into spoken situations.
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Reading is less frightening, less pressured, less challenging than speaking. You have more time, more pick it up and put it down-ability. This means that when you struggle to read, and then succeed, you think your struggles are over, but you’ve got another struggle still ahead of you. If you do the tough bit first - speaking and listening - then the reading challenge will be easier (still a challenge, but you’ll see it as “learning to read” rather than “learning the language” which will make things easier.
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It’s how you learnt your first language. You spent ages learning to understand stuff around you, and then started using words yourself, making lots of mistakes, getting corrected, more often correcting yourself as you got used to patterns and realsied you were mis-using some of them. Then you learnt to read, and then to write. Do it that way round as an adult as well - it seems to bring the language into a more natural place in your subconscious.
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Reading takes time. Until you’ve finished course 1, you should be using all your spare learning time doig lessons - they’ll be far more beneficial to you in the short term, by increasing the number of patterns that you have to hang all your new vocabulary on. Use your time wisely!
Here’s a quetion - how far are in you into the course? If you are already into course 2, and are desperate to start reading some books taht you’ve seen and think are fascinating, then why not? On the other hand, wherever you are in the course, if you just feel that somehow you’ve not learnt the language until you can read as well, then keep on learning to speak - reading is fun, but it’s not what learning a language is about!
That was a bit longer than I’d intended - I hope you got to the end of the post. I expect someone has posted exactly the same but in two or three lines as I’ve been typing - it seems to happen quite often… 
Oh yes, and enjoy the challenge of speaking your new language. It’s a real achievement!