It looks like the museum is open 1 April to 1 November:
Daily 9:00 to 22:00. Ticket times run from 09:00 to 20:45. I'm guessing that prior to 1 April when there are no later tickets available, it's because of the earlier closing times. After that, they are sold out.
Using 1 March as an example, there are lots of tickets available for the early morning time slots. Using 24 April, 2 months from today, there are some tickets available in the afternoon up to 17:45.
I think the website is very confusing. So I just messed around with the ticket buying page. If you go there, the results may be different by the time you do it. I'm going to try it after midnight Amsterdam time to see if that's when the day changes for their website.
Thank you so much for asking this question. I'm planning for either an early or late June visit. Of course right now is too early to get online tickets for those dates. I'm guessing that you might be able to see your mid-June date the same day in April.
I'll certainly be checking my early June date on the same day in April. It appears that the available dates and times for the 30 Minute Program + Museum Visit are much more complicated, so I may have a steeper learning curve.