Usually when you want to speed up say your air defence upgrading and it cost 218 gems but you only have 209.... well this shouldn't stop a clasher from speeding up the time
My idea is that you should be given the option to speed up things with the amount of gems you have so using the example before if you were to press the air defence while it is upgrading instead of it saying speed up for 218 gems it would give you the option of speeding it up for what you have. So it'll say or speed it up by 2 days 14 hours for 209 gems.
