How long for contact cement to cure?

How long for veneer to stick to wood via contact cement.

It's not my project, so choice of materials are limited. But thankfully we did some tests first.

Baltic birch ply
Walnut veneer with paper backing
Lepage gell contact cement because that was the only one in the store.

We tried three different ways.

1. Spread on both sides extra thin.  Put together immediately.

2. Spread both sides, pretty thin, wait 15 min, put together

3. As instructed by the tin, spread on both sides generously,  repeat after 15 min until both sides are shiny, wait 15 min, stick together.

Follow by pressing well with a back of the spoon to smooth it because the stupid roller bryer thing is hidden.

Since max open time is one hour, first test was then.  Easy to take apart. No damage to surface, only glue failed.

Second test at about 18 hours,  almost as easy to remove.  Again glue failure.

Thrid test was more than 48 hours,  slight effort to take apart, pure glue failure.


This was done on a flat sample.  The final project is more complicated in shape and needs an instant stick glue, thus the person insists on contact cement.   But it doesn't instant stick as described.

Do i just need a longer curing time?