one can't afford doing or continue doing a certain action because of nervousnes or to meet the demands of that particular situation or moment. 「〜てばかりはいられない」is almost the same as 「〜てはいられない」, only the ばかり emphasizes of " only just doing .... (action that one should not be doing that moment)".
In #5856, "Since the customers will be coming in no time and it will be a hard time" is awkward. Should read: "Since customers will be arriving in no time and we will have more than our fill..."
Sorry if this is too simplistic, but am wondering if I can use this with the negative form as well? For example, can I say "___ しなくてはいられない" (Can't afford not to do __)
If you want to say you cant afford not to do, you should probably use I must do or have to grammar forms. English and Japanese don`t have the same idiomes, so trying to translate your thoughts exactly will end up in strange Japanese. when you want to say Can`t afford not to do try
しなくではいけない (I must) or しなくではならない (I have to)
also if you want to add a hypothetical if to it しなければいけない or しなければならない