A Husband in Time — Maggie Shayne

THE STRANGER
The man had come to Jane Fortune from out of nowhere. He couldn't explain who he was, but Jane's young son could. The little boy insisted Zach was his imaginary daddy come to life, the father he'd always wanted. And even Jane couldn't deny that he was oddly familiar --- and the husband she'd always dreamed of. Yet the clock was ticking on the family they'd formed, because Jane had discovered exactly who Zach was. And only a twist of time could keep him home.

FORTUNE'S CHILDREN