From the circumstances you described, you could certainly argue that the waiver is not valid. In previous experience, companies I have worked for have always given people time to think over any waiver and also would give them the time to consult a solicitor before signing. Your husband should contact the employer right away though, before taking steps towards a claim - the longer a waiver stays out there, the more likely it is that he would be deemed to have accepted it. So the first step to take is for your husband to call and write to the employer and say that he is not satisfied with the terms of the waiver and the time he was given to consider it and that he'd like to come in to talk to them about it. If those discussions don't bear fruit, then have a chat to a solicitor.
Sprite