I've heard of speed breeding which makes use of optimal circumstances in glasshouses and growth chambers. Is it also possible to shorten a plant's maturity time (i.e. the time it needs from being planted until the time its yield can be harvested) using genetic modifications?
Perhaps investigate the families of YUC genes that synthesize the growth hormone auxin (ncbi.nlm.nih.gov/pmc/articles/PMC6941117) and ARF genes (ncbi.nlm.nih.gov/pmc/articles/PMC4737911) that respond to auxin. Auxin overproduction or changes to ARFs might speed growth. But some herbicides are synthetic auxins (e.g. 2,4-D) and work by exhausting and killing weeds (en.wikipedia.org/wiki/2,4-Dichlorophenoxyacetic_acid), so modifying these pathways may have unwanted side effects, depending on the crop.
Independent of the hormone manipulation suggested by Alex Reynolds, perturbation of transcription factor UPB1 has been found to have an effect on plant growth by Tsukagoshi and colleagues -- Transcriptional regulation of ROS controls transition from proliferation to differentiation in the root.
In short, disrupting UPB1 activity in model Arabidopsis roots alters the balance of free radicals, leading to delayed differentiation and continued cell growth. UPB1-deficient roots were faster growing and composed of larger cells. Artificially increasing UPB1 activity resulted in slower root growth.
Taking OP's definition of maturity time --
the time it needs from being planted until the time its yield can be harvested
-- the agricultural utility of this mutation depends on the crop. If the goal is to increase the amount of biomass as fast as possible, this is likely a beneficial mutation. If the goal is to decrease the time needed for a plant to bear mature fruit, this mutation would not be ideal, given that disruption of UPB1 activity leads to slowed cell differentiation.