Is it overreaching?

You can (and should) ask for whatever you want - whether the vendor will agree to it is another story. That's why you do your due diligence when selecting a contractor and get everything in writing.

I believe ANY repair or home improvement project should have a start and end date, along with:

language on how changes are to be handled
specifics on what will be done, the type and quantity of materials to be used
who cleans up after the project is finished
a lien release from all subcontractors (so they won't put a lien on your property if they don't get paid by the main contractor)
who gets the permits (ultimately it's homeowner responsibility, so if the vendor says he/she will do it, get it in writing and be sure to inspect it before the work begins
a payment schedule (don't pay more than 20% at the start and don't pay the balance until after you've inspected the work, the area has been cleaned up and you have documentation that all liens have been released from all subcontractors

There's more, but that's a start.

I would not agree to the 10% either. Maybe more like the job shouldn't go over a 20% threshold of overall costs. Meaning they can't just start tacking on charges. It's reasonable if they find something that needs fixing along the way or additional materials. However, if it's going to add another 20% to the overall cost, then I would make that another contract for repairing. A contractor can't predict what issues/expenses they may run into when doing a project. So should build in a bit of a bumper.

Be careful of some contractors who want to add on their own expenses. There are certain things that is the nature of their job. Like if they are painters. Their paint brushes all go bad doing your job. They now want you to pay for their replacement brushes. I would say "no". The nature of their job are they are painters. It is the cost of them doing business. However, if they run out of paint then HOA pays for that.

I bring that up due to my ex-president who was a con man. He'd often bid out jobs and low bid them. However, along the way he would add on additional expenses and pass them onto the customer. So at the end the customer was paying for much additional work or expenses. They were things like his own supplies. So just be aware if you run across someone like that. Supplies should be things that involve the job itself, not something the contractor can walk away with IMO.

It is not unusual for large public and private projects to include performance bonuses for meeting schedule goals, or to have penalties for missing them. 10% per day seems extremely excessive. If the project is completed 10 days late, the contractor works for free. If you can get anybody to agree to this, hire them on the spot and make it difficult for them to complete on schedule.

The 'product' may have a 25 year warranty (similar to roof shingles ?!), but, what about the labor ??!!!!

eg. your 25 year $20,000 roof fails after 5 years and the 'shingle company' ships you $3500 in shingles

..... just sayin'

my HOA had the issue with 'fibre-tech' lining - we received $2950 worth of 'product' after spending $29000 for the total installation when it failed at 4 years (possibly due to faulty installation)

correct

The key legalese is:

"Time is of the essence." Work to be completed no later than xx/xx/xxxx.

Penalty for each 24 hour period late is {negotiable amount / % of contract / whatever}.