The は particle has two primary functions. The first is to mark the topic of a sentence, as learned very early in our Japanese language journey. However, the second common usage of は is to highlight contrast (making a comparison). When は is used after a number/counter, it regularly has this comparison meaning. This can be translated as ‘or so’, or ‘at least’.

• ディズニーランドには年（ねん）に5回（かい）は行（い）っている。
  I go to Disneyland at least 5 times a year.
• 私（わたし）は毎日（まいにち）、テレビを5時間（じかん）は見（み）ている。
  Every day, I watch TV for 5 hours or so.

Before は, the counter is regularly followed by くらい (or ぐらい). This just softens the statement, and further highlights the ‘or so’ meaning.

• 2キロくらいはあると思（おも）う。
  I think it is at least 2 kilograms.
• 倉敷（くらしき）には1回（かい）ぐらいは行（い）った方（ほう）がいいよ。
  You should go to Kurashiki at least once.

Despite being translated as ‘at least’, the comparative meaning of は itself is what creates the nuance of this grammar structure. The thing before は is being highlighted as an amount, while also implying that there are other amounts. This implication of another amount makes は sound as if it could mean ‘as opposed to (B)’. So in essence, this grammar structure sounds like ‘As for (A), as opposed to (B)’, where (B) is not usually mentioned.