Typically in pharmacology after five half-lives a given substance is considered fully eliminated. However, it depends on the nature of the screening test. If metabolites are tested as a surrogate for the substance in question, the half-life calculation should be based on the metabolite, which may be much longer lived. This seems to be the case in the case of BPC157. There's a journal article from a few years where they propose using a solid phase extraction method and gas chromatography/ mass spectrometry for detection and quantification, which measures to a threshold of 0.1 ng/ml with a precision of less than 20% (which is pretty poor performance from a statistical perspective) and is stated to be able to detect up to four days from last use:
https://www.researchgate.net/publication/311975846_Detection_and_in_vitro_metabolism_of_the_confiscated_peptides_BPC_157_and_MGF_R23H_Detection_and_in_vitro_metabolism_of_BPC_157
There is another study of metabolism in rats and dogs from 2022 which shows rapid breakdown of even the metabolic products, with most of the amino acids appearing to be recycled by the body into other uses.
https://pmc.ncbi.nlm.nih.gov/articles/PMC9794587/
In this study they used isotope labeled proline as a tracer (with two of the hydrogen molecules on the proline carbon ring replaced by tritium) since measuring the direct metabolic products is difficult.
Anyway, on the gripping hand, detection is an expensive and relatively exotic procedure, so unlikely to be used unless you're an athlete with mandatory testing under the WADA rules. It that is your setting, it may be of benefit to carefully consider the risks and benefits of peptide usage, and in any case, your urine is likely below detection threshold after four days, particularly if you stay well hydrated.