You'll need to be lucky. Everything will depend on whether your 7pm-arriving bag reaches the delivery distribution point by about 9:30pm, since the drivers do not pick up after that and the entire delayed baggage facility closes at 10:00pm and everyone goes home. If your bag doesn't get there in time, it won't be sorted or picked up for delivery by a driver until 7 or 8 am and probably not leave the airport before 9am. Such are the vicissitudes of delayed baggage at LHR since they instituted closing the service at 10pm each night. I hope you are lucky.