Shipping big WAL archives to hot standby

I'm looking to extend my PostgreSQL 9.4 master with a few slaves in hot
standby read-only for load balancing.

The idea would be to update the slaves only at defined times (once every
24/48 hours) to avoid migration issues with the application server code
and also because the "freshness" of the slaves is not so important.

What would be the effect of suddenly introducing a 1-2 GB of WAL
archives to the WAL restore folder on the slave? Would there be a big
performance effect on the incoming queries to the slave? Would the slave
be available for queries while the WAL logs are restored into the DB?

Thanks
Jordi