There are 2 books in the Time series series. The newest book is From Time to Time which came out in 1995.

1
Time and Again

Book cover of Time and Again
Si Morley is bored with his job as a commercial illustrator and his social life doesn't seem to be going anywhere. So, when he is approached by an affable ex-football star and told that he is just what the government is looking for to take part in a top-secret programme,…
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2
From Time to Time

From Time to Time
In the long-awaited sequel to Time and Again, Ruben Prien is attempting to prevent World War I--but the man carrying papers to America that might avert the catastrophe is traveling aboard the Titanic. 125,000 first printing.