1950/60/s children's book - caves/labyrinth permitting time travel.

I'm trying to track down a UK (?) children's book I read in the 1960s. It involves two boys or young men finding a maze or labyrinth from which various exits allow them to explore the past. I seem to recall them meeting a caveman within and following him to explore his time and world. At the end they encounter someone from their future who bars their way. The book title may include the term 'maze' or 'labyrinth'.
The book was a hardback and available in late 1960s England. I can’t find ‘hide nor hair’ of this excellent novel on the web and would love to read it one more time. Any help to that end would be enormously appreciated.

How about The Time Maze by Reginald Maddock? There doesn't seem to be an entry for it in Librarything but the description in Goodreads is:

Two young boys fall into a cavern while bushwalking, and discover the cavern leads to a maze that can transport them to different eras in time.

Dear indybr12 - you've done it again! (For others: see my thread commencing 31st Oct. re 'Historical novel set in Late Roman Britain') And have thus acquired, as promised, official 'Very Wonderful Indeed' status.

These two conundrums have been troubling my early hours thoughts for decades! Not to mention losing me untold hours in fruitless Google searches. I really do thank you for taking the time and trouble to resolve them and I commend your searching skills.

I'm almost positive that it was Maddock's 'The Time Maze' as you suggest and I've snapped up the sole copy (!) - and even that jacket-less, alas - available on Amazon.

Now that the problem's solved I don't see how I didn't stumble across it myself after innumerable searches on 'maze', 'caves', labyrinths etc. etc. However, hitherto, for some reason, it was occluded from me - until now.

Thank you so much again. JAW.

You're welcome, JAW. How fortunate that you were able to find a copy! It's a wonderful thing to rediscover an old favorite book. I'm happy I could help. - indybr12