First Ax we use the 40 hours as a "guild line" its not written in stone some builders have to wait longer some get promoted earlier but we have it there so as to make sure they are actually going to stay with us and not just trying to get promoted really quickly then leave forever (we have had that issue). But if the person shows his/her ability to actually build really amazing things or not and just build single line towers we see that and promote accordingly.
Secondly though you have made some really nice things, the shuttle and the bowers/koopa thing being really nice it's not quite enough to get promoted but you are on the right track! Just keep at it and you'll be there in no time!