No está el horno para bollos

[ROBINDESBOIS]

Significa que no están los momentos para permitirse ciertas bromas, o acciones. Mejor andarse con pies de plomo.
ENGLISH?

[poli]

This is no time for comedy.

to land like a lead balloon.
Example:
Your joke at the funeral about embalming fluid landed like a lead balloon.

[bobjenkins]

This is not a laughing matter
This is no time for jokes
This is no time for joking around

[ROBINDESBOIS]

Gracias a todos

[bobjenkins]

De nada, aún no creo que la rapidez a la que estás aprendiendo :D Es bueno!

[ROBINDESBOIS]

Tu también.

[aleCcowaN]

No está el horno para bollos = It's not the right time to do that. The circumstances are not propicious. The general mood won't welcome those ideas.

- Mamá, necesito dinero para irme de vacaciones con mis amigos.
- Ni lo menciones. El horno no está para bollos. A tu padre le acaban de chocar el auto y el seguro no cubrirá todos los gastos.

[poli]

There are a few phrases in English that approximate the usage.
Not ripe for the occasion can be used in the following way: In defending a major case, a lawyer just out of school may not be ripe for the occasion.

In your example this term wouldn't work. Instead, mom would say, Now's not the time. Your father just had a car accident and insurance won't cover all the expenses.

There are other terms less common such as you can't force a flower to bloom often having to do with forcing someone who is not ready to do something.

[aleCcowaN]

Cuándo el horno no está para bollos es mejor andarse con pies de plomo.

When the situation is volatile
/ is everything but favourable/auspicious, it is better to tread carefully/proceed with caution/try and avoid being conspicuous.

[poli]

Leaden feet means the exact opposite in English. Tread lightly is the terms used in English.

[aleCcowaN]

Leaden feet means the exact opposite in English.

That's very good to know. I suppose it is like "andar/venir pisando fuerte" in Spanish. Figuratively, decided steps that crush obstacles and discourage opposition.