Save this as a bookmark, making sure to update “yourbasecampurl” and “yourid” accordingly…

javascript:var%20t=new%20Date();t.setMonth(t.getMonth());var%20m=t.getMonth()+1+'';
var%20y=t.getFullYear()+'';var%20d=t.getDate()+'';if(m.length==1)m='0'+m;if(d.length==1)d='0'+d;
location.href='http://yourbasecampurl.com/time/report/yourid/'+y+m+d;>

You can work out your id by generating a time report for yourself and looking for the number after ”/report/” in the url. It looks to be 6 or 7 digits long normally…

Update: Works fine in Safari and Firefox