I've found it important for our dc to finish an HOD guide to be ready for the next guide. The maturity of content and skills generally increases in progression within a guide, and by missing the last third of LHTH, I think you'd be missing some important things.

LHTH is a chronological journey through time from Creation to Paul's Missionary Journeys. Unit 22 begins with Jesus' birth, His ministry and miracles, His death and resurrection, and ends with the spread of the Gospel. We found this progression to be moving and a great foundation for beginning LHFHG, which begins at creation but moves much more quickly through history to end with the 1970's. Much less time can be devoted to this all-important time of history in LHFHG, when our Savior was born and changed the world.

Obviously this is a more mature topic as well. The math skills covered in the last third of LHTH are more difficult as well, and cover a variety of skills...
21 - tracing or copying designs and finding shapes
22 - counting: one to one correspondance
23 - comparing numbers: more than/less than/equal to
24 - counting and addition combinations that equal 5
25 - general measurement: area
26 - nonstandard measurement: “feet”
27 - sorting, counting, and graphing sets
28 - money: coin recognition, value, counting
29 - general time: yesterday, today, tomorrow
30 - number sense: more than 1 and counting forward/backward
31 - counting forward/backward and early addition
32 - general fractions: whole vs. part
33 - sorting and classifying: color, size, and shape
A final few reasons I'd finish LHTH are often dc's writing skills come much later than reading and math skills, and this may show itself as a hurdle later in the subsequent guides - and finally, teaching dc that finishing a guide is in itself an excellent thing to do.
So, for these reasons, I'd finish LHTH, but possibly add phonics instruction. I think you could definitely do 2 lessons of LHTH each day as well, as this would still accomplish completion of the guide and all its content and skills. HTH as you ponder what to do, and congrats on having a happy little one that loves learning and is thriving!
In Christ,
Julie