Hakim al Umma Mawlana Ashraf ‘Ali Thanawi (Allah have mercy on him) said,
‘Time management and planning how to to do so are a great things.
It should not be the way to do something in the time allocated for another thing and do that particular thing in some other time slot.
Everything should be done in the time set for it.
This brings great blessings (barakah) in time (more things are done with ease in same duration) and comfort (to all).’
Husn al Aziz, volume 2, page 412
What if certain tasks take longer than you expect?
as salamu alaykum wrwb
If this is a rare occurrence than moving into another time slot will be fine, provided that the other schedule is maintained.
If this happens frequently then it will be better to revisit the whole schedule and make it more practical by increasing time allocations or reducing the stuff needed to be done.
Guidance from someone with experience is always beneficial.
muhtaj e dua