When creating a fantasy world it is important to include the developement of magic into the history of the world. The designer has to be able to explain the effects of various magic spells and magical items on the various cultures, world history and it's relationship to technological development. In worlds with rare and weak magic, the effect will be minimal to none. With more common and powerful magic the effect is noticable. The D&D d20 rules presume significant amounts of magic, spell casters and magical items that the effect on history should be significant.
This time line only covers spells that became well known and wide spread. It is entirely possible for a spell or permanent magic item to have been invented many centuries before, but it was never shared widely and thus faded from memory. A real life example would be concrete that was invented by the Roman Empire, but lost until the last two centuries.
The first magic spells were granted to small numbers of people who had accepted the gods on Oceana over the gods of their home planet, especially Earth. The spells were mostly healing and crop spells.
For example, if magic is better, or provides significant protection from early firearms, then there will be limited development of firearsms. This is the case on Oceana. Magic was sufficiently developed and common when gunpowder and firearms were introduced to Oceana. This coupled with the expense of
protective magic armor sufficent to render early guns obsolete has to exist prior to
protective spells for ships against early cannons must be in place prior to gunpoweder and cannons
move earth and stone spells have to exist and be more powerful and cheaper than early cannons. castles should probably be outmoded before gunpowder makes it to Oceana. cities would still have walls to keep out raiders, but not the kind of depth to protect against major seiges.