One of the co inventors of the nerve agent has now said that due to the complexity of the nerve agent and the difficulty in deploying it , only the Russian state itself can be responsible.
https://www.reuters.com/article/us-britain-russia-scientist/only-russia-could-be-behind-u-k-poison-attack-toxins-co-developer-idUSKCN1GP2ZK
So do you still think it was not Russia that did it ?
This says that 'delayed onset' is possible if the agent is deployed in a way that facilitates it
What does Novichok do to the body?
It is generally dispersed as a fine powder, though there could be a number of ways a carrier on the ground could disperse a powder. Details on the dispersal technique regarding Sergei and Yulia Skripal are still unknown.
Once it hits the body, it penetrates the skin and can be breathed into the lungs. The victim can expect to show symptoms in under two minutes, often within 30 seconds. However, depending on how the agent is weaponized, delayed onset is possible.