Tory Rebels....

You can't just sit there and do nothing as PM. If the Lords screw you then you must threaten to use the Parliamentary Act. The fact is many MPs are traitors to the country and many are in the Tory Party now. They are just on the make like Johnson was. Anyway, if the bill fails to stop the problem one will have to make amendments to correct the trouble. For example if the ECHR lawyers try and exploit it we threaten to leave and then they will be out of a job. 

On the one hand it is a fair statement that a Prime Minister under pressure from the House of Lords should at the end of the day consider the use in extremis of the Parliament Act.

Let us suppose for example that Theresa May’s utterly disastrous antics after Cameron’s cowardice led to Boris declaring in 2017 that he WAS in fact that man, and that his overwhelming majority in 2019 earned in the face of years of trench warfare by the opposition in collusion with the Speaker to thwart the will of the people came two years earlier. Had the Lords then begun a conspiracy to thwart the manifesto commitment to ‘get Brexit Done’ it would have been both righteous and democratic to use the provisions of that act to crush the opposition in ‘that other place’

BUT

It is one thing for a newly elected government (or even a government of some years standing), elected with a massive majority with a clear manifesto commitment upon which the overwhelming number of government MPs stand resolute in support of, to use that Act to push through a measure which they were elected to implement. It is also conceivable that a replacement leader of the party, chosen by that party’s publicly declared mechanism, who enjoyed the continued support of the back benches for the policy in question to use that measure to remove the blockage imposed by the unelected house ….

However it is quite another for a man rejected by his party’s leadership process, beset on all sides by differences of opinion in his backbenchers, despised by his party membership for several reasons, not least his abuse of that leadership process to seize power, whose economic policies have crucified his own party members and whose so called flagship policies have each and every one been dashed to pieces on the rocks of political and legislative reality, to seize that legislation, as a drowning man seizes the thinnest and most unsuitable of overhanging twigs dipping into the maelstrom, and abuse it to impose his dictatorial will.

After all, this country had a record of going to war to remove such people from power.

Im not sure what he is trying to do is even allowed ?  The separation of government and judiciary is clearly divided to save us from tyranny .If he can as you say overturn convictions for post office victims overnight whats to stop him bypassing the judiciary in other matters ? 
Though I think we would all agree the post office people need justice that has to come from the courts not from a PM deciding their innocence because that will lead to him in the future deciding someones guilt.

It will be going through Parliament - possibly in about 6 weeks time

Sunak is not personally overturning convictions, a new primary law will shortly be introduced to exonerate convicted postmasters , this new law will go through Parliament as usual (but should be supported by all sides)

I think you rather answer your own question there. No-one will oppose the Post Office Bill. Everyone, including both wings of his party opposing his Rwanda Bill. That's why it will take time.