server: calculate checkin return time more accurately
server: calculate checkin return time more accurately

ha/doozer,tempbottle/doozerd,soundcloud/doozerd,npchp110/doozerd,bitly/doozerd,coreos/doozerd,soundcloud/doozerd,zyxar/doozerd,coreos/doozerd,jmptrader/doozerd,tempbottle/doozerd,ha/doozerd,ha/doozerd,npchp110/doozerd,rowhit/doozerd,zyxar/doozerd,magastzheng/doozerd,coreos/doozer,jmptrader/doozerd,tempbottle/doozerd,jmptrader/doozer,magastzheng/doozerd,zyxar/doozerd,rowhit/doozerd,soundcloud/doozer,rowhit/doozerd,ylong/doozerd,ylong/doozerd,npchp110/doozerd,ha/doozerd,jmptrader/doozerd,jmptrader/doozerd,bitly/doozerd,npchp110/doozerd,magastzheng/doozerd,ylong/doozerd,soundcloud/doozerd,magastzheng/doozerd,npchp110/doozer,zyxar/doozerd,ylong/doozerd,tempbottle/doozerd,soundcloud/doozerd,soundcloud/doozer,coreos/doozerd,bitly/doozerd,rowhit/doozerd