Translation:Let's make it in four days!
만들어 = informal low 만들어요 = informal high 만들자 = formal low 만듭시다 = formal high
what stops it from being a command? shouldn't "make it in four days" be accepted?
Nothing! In polite (~어요/아요) form, statements, questions, commands and suggestions sound the same. However, one usually adds the honorific particle while giving a command to not sound too rude. Henceforth command 'make' would rather be 만드세요, not 만들어요.
Also note that the 'ㄹ' gets deleted from the end of the verb stem (만들) when directly proceeding the '세' particle
Is this a "let's make it, starting in four days time" or a "let's make it over the space of four days" or are both valid interpretations?