Make sure the flowers are dry enough but not crispy dry, because if you put them in the jars while they are still too wet, can lead to mould. Putting holes in the lid will allow your flowers to dry out too much. "Not burping" your jars while you are away will not be a big issue. Hope this helps.... Organoman.
PS - Try leaving the healthy green leaves on your plant and only remove the yellow leaves. Less healthy green leaves = less energy produced = smaller flowers.
Cheers!