The standard error we see here all the time is confusing amps and amp-hours.
Amps are what is happening right now. Amp-hours are the average amps over a time.
The analogy with plumbing is that amps are gallons and amp-hours are how many gallons you get over time.
Your 600 watt 12v toaster would be 600 divided by 12 or 50 amps, plus the probable 15% inefficiency of the inverter so closer to 60 amps. 5 minutes run time is 1/12 of an hour, so the amp-hours is 60 divided by 12 or 5 amp-hours that your 100 amp hour battery will go down.
Recharging it will depend on how far down it will be. If you are under about 70% full, it will charge at close to what the solar will put out, so yep and hour at 5 amps to give 5 amp-hours back. If it is at 90%, it might take 3 hours because the charging slows way down as AGM batteries near full.
It is also likely that you will see a lot of voltage drop on smallish battery for that size load. Depending on the settings for low voltage cutoff of the inverter, it is likely it would not be able to handle that load at less than 50% full without tripping out.
When calculating power use in amp-hours, like the battery is rated, it is always amp times the hours those amps run, which can be over or under an hour.
Also remember that about 80% discharged is about as low as you want to go with an AGM, and they need to be fully charged every 7-10 days if in cycling use. A full charge can easily take 6-8 hours or more.