Employers have until tax day to fund matching for the prior year, as an employee your contributions end 12/31 of that year.
Most 401ks plans have a max on the % of your paycheck you can bump contributions to, for example, its 65% of paycheck where I work now. Have seen 80%.
Most employers match per paycheck, meaning you won't get any serious match benefit if you were already doing at least 8% before. Maxing out early aka front-loading only works if the employer does a "true up" match. Mine does, I know of others that do not. It's in their benefit from a tax perspective to do so, but its also a hassle for them to go through and calculate. My true-ups from front-loading are deposited March of the following year (before tax day) (somewhat negates benefits of frontloading because you receive match later). If you won't still be employed there you probably won't get the true-up match deposit to your account.
A few things to consider: 1) your single employer will cut you off at 18.5k. A new emoloyer will have no prior knowledge of your contributions so you'll need to tell them to cut you off at your remaining contribution, or manage it very carefully yourself. 2) Figure out what you want to do with your old 401k. Rolling it into an IRA has implications for back door roths if you ever expect to be earning over the Roth contribution cap. Rolling into the new employers 401k preserves back-door-ROTH flexibility, but may have worse investment options/fees.
