How should I deal with a colleague talking on my behalf?
I'd suggest putting in those days - they may or may not be lost, but losses occur*. No use crying over spilt milk. Writing the time down as lost means, you can be happy if something good comes out of them at the end. OTOH, aking a fuss creates a serious risk of a trench war that would cost much more time.    

However, I'd also talk to him in a calm minute. I may be taking a line saying that he luckily foresaw the way my opinion went, yet I'd wish him to quickly ask me beforehand in the future.
Talkin calmly may need that you know exactly why you are so angry that you have to post in a public Q&amp;A site. 

* partiuclarly in writing proposals. There's a rumour here in Germany that the Bundesrechnungshof once estimated that for different kinds of public grants from a national economic point of view (i.e. including all proposals that are written: accepted as well as rejected) about as much money/effort goes into writing grants as is distributed by the different grant programs (estimates ranging from 1 : 2 to 2 : 1 are mentioned).