Does anyone know if there is a deadline by which time offers are made?
It's on the UCAS website
www.ucas.com/undergraduate/after-you-apply/ucas-undergraduate-types-offer
When are you likely to hear back from unis?
The wait for decisions on your application can be agonising. It’s a good idea to use this time effectively by familiarising yourself with the decisions the unis you’ve applied to could make, so you know what to expect and what to do when the time comes.
Each university and college will make their decisions at different times, meaning you might hear back before your friends do, or vice versa. However, there are deadlines by which they will need to have decided:
2019 entry
2 May 2019– if you sent your application by 15 January 2019
11July 2019– if you sent your application by 30 June 2019.
22October 2019– this is the final deadline for unis to make decisions on applications to courses starting in 2019.
If a uni you’ve applied to doesn’t make a decision by the appropriate deadline, that choice will be automatically made unsuccessful.
Apart from some medical school decisions, I think most responses to on-time applications are usually received by the end of March, though. TSR usually has a thread on 'Fastest and slowest offer senders'.