If a time-leap is mere matter of days, weeks, a month even then it’s relatively easy to pass off by way of character interaction, momentary character thought, or within brief descriptive passage relating to time and date etc., though not in the manner of a train timetable. Bearing in mind we have unpubbed authors following as well as pubbed writers, I thought I'd put forth examples of what we're talking about!
Last sentence: example.
. . . She watched his flight take off, heart in stomach for she hadn’t told him, and wouldn’t until his return.
Melinda had passed this way a dozen times over the past two weeks, always in a rush, head down against bitter east wind, snow underfoot, and not a flower in sight. Yet today, the wind had swung southerly. It was a glorious sunny morning. Ice crystals sparkled like diamonds and joy of joys snowdrops had emerged and gently ringing in the first week of February. Gosh, how time flew. Guy had been gone a month, and tomorrow his flight would touch down at Heathrow, and what then?
Simple: if we’d read the previous chapter we’d know why Melinda is always in a hurry, we’d know it’s wintertime, but it would have been just after Christmas when Guy left. Now it’s February, and Guy (whomever) is due back after a month’s absence. There’s even a hint of possible conflict brewing. BTW: the above snippet is straight off the cuff.
When a timeline amounts to a year or more, and a novel spans almost six years, I go for a “sub-heading” to define year and place: as in my latest historical. These timelines are always at the beginning of a new chapter.
Axebury Hall Estate: 1644 - Axebury Hall Estate: 1646 - Glastonbury: 1647. Axebury Hall Estate: 1649. Huge leaps like these, I think, require a definite timeline.
The one thing that really annoys me when reading a novel is to find a quarter-way into a new chapter that a timeline has occurred and the story has moved on several months or a year and not a mention of such having happened.
…Harry hadn’t attended the funeral. Why?
…“Oh for pity’s sake, Amy. Why didn't you leave Xander with the nanny?”
…Mark zapped the window button. The stench of city smog and garbage filled the limo. He didn’t know which was worse. The smell permeating from Xander's backside or rank smell of stale fish.
…Why him, why did they have to be in this forsaken sector of the city?
Reading this I started thinking when did Amy give birth? I went back over the previous chapter thinking I’d missed a page but no, not a mention of Amy and a baby! Where are they? Grrr...
OK, so Amy was eight months pregnant in the previous chapter, yet there’s no explanation as to how old Xander is, yet Amy is a lead character. Then, five pages later it comes to light it’s Xander’s birthday. (How old?) No clue until page eight. Guess what, he’s two! By Chapter three I discover they’re in Hong Kong.
So what does every one else do when a timeline occurs? Hope a reader grasps a descriptive prompt, afford vague reference, or leave them to puzzle it out?