I totally agree with Evgeny that “идти лесом” here is one of those funny genteelisms where one is sent "в лес", "в баню" or "на хутор бабочек ловить" instead of naming the actual destination ;) On the other hand, in the offered context it can hardly be considered an obscenity, rather an expression of some casual disdain at one’s unrealistic expectations (like in "...by tomorrow? But are they kidding or what?"). It can be rendered in a variety of ways (and I am sure you'd find a better one, these are just some examples):
"And about getting it all cleared by not later than tomorrow – do they want jam on it too? / well, some hopes! / let them dream on / forget of it, etc."