Yes, you absolutely can! It needs to be done in writing, so make sure your agent does it immediately to avoid the seller signing your offer, which changes the story. If for some reason, you're too late, and the seller accepts your earnest money, you still have a few legal outs, i.e. financing contingencies, inspections etc. Make sure you have a great realtor who will educate you on these options should you find yourself in this situation!