u/pipeline77

Im looking to install a 18000btu unit at my house. Ideally, I would get the 50' line set, but the unit is only precharged to 25'. The manufacturer recommends adding 8oz to top up the unit. Unfortunately, the hvac installers around here dont seem to want to touch a diy job. Is 8oz difference going to be critical? Do I have other options for adding refrigerants? Thanks