I will preface this all by saying I am not a haiku expert either :) but, I have done some haiku translation work, both J>E and E>J, so hopefully I might have some helpful feedback.
What I like:
I like the break, from visual imagery in the first two phrases, to concept/thought in the third phrase. This is effective for me.
Also, I think the scene you describe lovely, in itself :)
Elements that you might want to think about more:
The main thing that stands out to me is the きーぎーき pattern in ending each phrase, which I feel leaves the verse a bit unbalanced somehow. I would personally rather there be a little more variation in the ending sounds.
I'm also struggling with imagining 七の雪 as I don't really know what the 七の is doing. I'm just imagining (heavy) snow...? (This is more likely down to my ignorance, so my apologies!)
I note that you don't use a verb in your haiku, which is totally fine. But, do consider them to create potentially more detailed description, movement, or more of a story (see point re. narrative below).
Lastly, if I am being most (subjectively) critical, I think maybe you could be more ambitious with the imagery and/or narrative?
Imagery-wise, for instance, bamboo is a plant that stands upright in winter, but also in autumn and summer, so maybe there is something that works better for winter specifically, if you are ending on the thought 冬の時. What might be some seasonal imagery specifically seen in winter?
Also, if you want to make a 'bigger point', perhaps there are things that you might tie the imagery to more metaphorically? For example, to use your 鷺, if you are looking at a white heron in the snow, you maybe can't see it very well; how might you describe that sensation? If you see just the flash of the heron's yellow beak, what else you could tie this to metaphorically or visually? (e.g. what else is fleeting like that flash of yellow?).
Narrative-wise, you don't need to have a "story" at all, but those haiku that use a strong narrative often have a sense of completeness about them.
I would think of an example of a more "story-like" haiku would be Bashō's famous
古池や 蛙飛び込む 水の音
This is probably just a different approach to the one you have taken, so it probably doesn't apply to this poem, but you might want to experiment with a more story-like approach too :)
So, those are just some thoughts, both general and specific. In any case, it is very easy to criticise haiku, whereas it is much harder to compose them, so thank you for sharing! I hope that helps!